Cardiomyopathy in Cats: Types, Symptoms, Treatment and Life Expectancy

Cardiomyopathy in Cats: Types, Symptoms, Treatment and Life Expectancy

By Dr Duncan Houston

A cat with cardiomyopathy may look completely healthy. Another may suddenly develop rapid breathing, collapse or lose the use of their back legs.

This is because cardiomyopathy is not one disease with one predictable outcome. It is a group of conditions affecting the heart muscle, and each type changes the heart in a different way.

The most important questions are not simply whether your cat has cardiomyopathy. You need to know which type is present, whether the left atrium is enlarged, whether congestive heart failure has developed and whether there is a significant blood-clot or abnormal heart-rhythm risk.

Quick Answer

Cardiomyopathy means disease of the heart muscle. The five main feline cardiomyopathy phenotypes are hypertrophic, restrictive, dilated, arrhythmogenic right ventricular and nonspecific cardiomyopathy.

Some cats remain symptom-free for years, while others develop congestive heart failure, arterial thromboembolism, fainting, abnormal heart rhythms or sudden death. Echocardiography is the main test used to identify the type and stage of disease.

Open-mouth breathing, marked breathing effort, collapse or sudden painful weakness or paralysis of one or more legs requires immediate emergency veterinary care.

What Is Cardiomyopathy in Cats?

The word cardiomyopathy can be broken into:

• Cardio: heart

• Myo: muscle

• Pathy: disease

A cardiomyopathy is therefore a disease in which the heart muscle is structurally or functionally abnormal.

The heart may become:

• Abnormally thick

• Stiff and unable to relax

• Thin, weak and dilated

• Scarred

• Infiltrated with fibrous or fatty tissue

• Affected by a combination of changes

Modern feline cardiology classifies cardiomyopathies according to the heart’s phenotype, meaning what its structure and function look like on echocardiography. This is useful because the underlying cause is unknown in many cats and different diseases can initially produce similar clinical signs.

Is Cardiomyopathy the Same as Heart Failure?

No.

Cardiomyopathy is the underlying heart-muscle disease. Congestive heart failure is a complication that may develop because of that disease.

A cat can have cardiomyopathy without being in heart failure. This is called subclinical or preclinical disease.

Congestive heart failure develops when pressure within the heart and blood vessels becomes high enough for fluid to accumulate:

• Within the lungs, called pulmonary oedema

• Around the lungs, called pleural effusion

• Within the abdomen, called ascites

• Occasionally around the heart, called pericardial effusion

Heart failure describes what the disease is doing to the cat. It does not identify which type of cardiomyopathy caused it.

How Common Is Cardiomyopathy in Cats?

Hypertrophic cardiomyopathy is by far the most common feline cardiomyopathy.

In the CatScan study of 780 apparently healthy cats, 14.7% were found to have hypertrophic cardiomyopathy during echocardiographic screening. The prevalence increased with age, although younger cats were also affected.

This does not mean exactly one in seven cats in every population has HCM. Prevalence varies with:

• Age

• Breed

• Genetics

• Body size

• The population being studied

• The echocardiographic criteria used

• Whether cats with secondary heart thickening were excluded

Restrictive, dilated, arrhythmogenic right ventricular and nonspecific cardiomyopathies are much less common than HCM.

What Are the Main Types of Cardiomyopathy in Cats?

Type	Main change within the heart	Important complications
Hypertrophic cardiomyopathy	The left ventricular walls become abnormally thick	Left atrial enlargement, heart failure, blood clots and arrhythmias
Restrictive cardiomyopathy	The ventricular muscle becomes stiff and fills poorly, often because of fibrosis	Marked atrial enlargement, heart failure and blood clots
Dilated cardiomyopathy	The ventricle becomes enlarged and contracts weakly	Low cardiac output, heart failure, arrhythmias and blood clots
Arrhythmogenic right ventricular cardiomyopathy	The right ventricle becomes thin, dilated and affected by fibrous or fatty replacement	Right-sided heart failure, ascites, pleural effusion and arrhythmias
Nonspecific cardiomyopathy	The abnormalities do not fit one recognised phenotype or contain features of several types	Variable, depending on the structural and functional changes

These categories describe what the heart looks like. They do not always reveal why the changes developed.

Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy, commonly shortened to HCM, causes part or all of the left ventricular wall to become abnormally thick while the ventricular chamber remains non-dilated.

The thick muscle may still contract strongly, but it often becomes stiff and relaxes poorly between heartbeats. The left atrium must then work against greater resistance to move blood into the ventricle.

Over time, this can cause:

• Left atrial enlargement

• Increased pressure within the pulmonary circulation

• Pulmonary oedema

• Pleural effusion

• Blood stagnation within the left atrium

• Intracardiac clot formation

• Arterial thromboembolism

• Abnormal heart rhythms

HCM may be obstructive or non-obstructive. Obstructive HCM occurs when abnormal movement of the mitral valve creates dynamic narrowing of the pathway through which blood leaves the left ventricle.

This obstruction can vary with stress, heart rate, dehydration and excitement. It does not necessarily mean that the cat has a worse overall prognosis than a cat with non-obstructive HCM. In the large REVEAL study, obstructive and non-obstructive preclinical HCM had similar rates of cardiovascular complications and death.

What causes HCM?

Primary HCM is believed to have a genetic basis in many cats, even when a specific mutation has not been identified.

Pathogenic variants have been confirmed in the cardiac myosin-binding protein C gene in:

• Maine Coon cats

• Ragdoll cats

Routine DNA testing is currently supported for the A31P variant in Maine Coons and the R818W variant in Ragdolls. A positive result indicates increased genetic risk, but it does not prove that the cat currently has HCM. A negative result rules out only the specific variant tested and does not replace echocardiographic screening.

Domestic shorthairs and other breeds can also develop HCM without a known testable variant.

Is every thickened feline heart HCM?

No.

A thickened left ventricular wall can also occur with:

• Systemic hypertension

• Hyperthyroidism

• Acromegaly

• Aortic outflow obstruction

• Severe dehydration or reduced circulating volume

• Myocarditis

• Infiltrative disease

• Transient myocardial thickening

Primary HCM should be diagnosed only after important secondary causes have been considered.

Restrictive Cardiomyopathy

Restrictive cardiomyopathy, commonly shortened to RCM, occurs when the ventricular muscle becomes stiff and unable to relax normally.

Unlike HCM, the ventricular walls may not be substantially thickened. Instead, fibrosis and abnormal myocardial compliance restrict filling.

The ventricles may appear relatively normal in size while the left atrium or both atria become markedly enlarged.

Two broad forms are recognised:

Myocardial restrictive cardiomyopathy

The ventricular muscle has impaired relaxation and a restrictive filling pattern without a large internal fibrous bridge.

Endomyocardial fibrosis

Prominent fibrous tissue may bridge parts of the ventricle, distort the chamber or interfere with normal filling.

Cats with RCM commonly develop:

• Pulmonary oedema

• Pleural effusion

• Left or biatrial enlargement

• Arterial thromboembolism

• Atrial or ventricular arrhythmias

In a study of 92 cats with RCM, 70% were already symptomatic when diagnosed, and most symptomatic cats had congestive heart failure. Greater left atrial enlargement was independently associated with shorter survival.

Can Restrictive Cardiomyopathy Be Temporary?

A transient restrictive phenotype has now been documented.

In a 2025 case series, 17 cats initially had echocardiographic findings resembling restrictive cardiomyopathy but later experienced resolution of the atrial enlargement and restrictive filling pattern. These cats were generally younger than cats with persistent RCM, and many had experienced a significant event shortly before the diagnosis, such as illness, trauma, anaesthesia or another inflammatory trigger.

This condition is called transient restrictive cardiomyopathy.

A transient form cannot be confirmed from the first echocardiogram. It becomes apparent only through serial examinations showing that the abnormalities resolve.

This is why a younger cat with an acute illness, increased cardiac troponin and an unexpected restrictive phenotype may need:

• Repeat echocardiography

• Serial cardiac troponin measurements

• Monitoring over several weeks or months

• Reassessment before a permanent prognosis is assigned

Persistent RCM and transient RCM may look very similar at the first examination.

Dilated Cardiomyopathy

Dilated cardiomyopathy, commonly shortened to DCM, causes the ventricular muscle to contract poorly.

The ventricle becomes enlarged, and the walls may appear relatively thin because they are stretched around a larger chamber.

This can lead to:

• Reduced cardiac output

• Weakness

• Low blood pressure

• Congestive heart failure

• Left atrial enlargement

• Blood stagnation and clot formation

• Abnormal heart rhythms

Is feline DCM always caused by taurine deficiency?

No.

Taurine-deficient DCM was once a major cause of feline heart disease. Recognition of the link led to the addition of appropriate taurine levels to reputable complete commercial cat foods, and the incidence fell dramatically.

Modern feline DCM is rare and is now seldom caused by taurine deficiency. However, deficiency remains important because it may be treatable and should not be missed.

Risk may be greater in cats receiving:

• Unbalanced home-prepared diets

• Dog food

• Diets not formulated to meet feline nutritional requirements

• Diets with inappropriate processing or ingredients affecting taurine availability

• Long-term food restriction or severe malnutrition

• An unusually restricted diet without veterinary nutritional oversight

When DCM is diagnosed, a detailed diet history should be obtained and whole-blood or plasma taurine may be measured.

Taurine supplementation is often started while results are pending when deficiency is reasonably possible because delaying correction may reduce the chance of recovery.

Can taurine-deficient DCM improve?

Yes, but improvement is not guaranteed.

Taurine supplementation and diet correction can produce major improvement in cardiac function when deficiency is the cause and treatment begins before irreversible damage develops. Historical studies documented meaningful clinical recovery and improved survival in taurine-treated cats.

Improvement usually takes weeks to months rather than days. The cat may still require treatment for heart failure and reduced cardiac output during recovery.

DCM that is not caused by taurine deficiency generally has a more guarded prognosis.

Arrhythmogenic Right Ventricular Cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy, commonly shortened to ARVC, is rare in cats.

The right ventricular muscle becomes damaged and is progressively replaced by fibrous or fatty tissue. The chamber may become severely dilated and contract poorly.

This can cause:

• Right atrial enlargement

• Tricuspid valve regurgitation

• Ascites

• Pleural effusion

• Liver congestion

• Weakness

• Fainting

• Ventricular or supraventricular arrhythmias

• Sudden death

In a pathological study of 12 cats, right-sided congestive heart failure was common, and several cats had ventricular or supraventricular rhythm disturbances. Left ventricular involvement could also occur, showing that the disease is not always restricted perfectly to the right side.

ARVC may be suspected from echocardiography and ECG findings, but definitive confirmation may require histopathology.

Nonspecific Cardiomyopathy

Nonspecific cardiomyopathy was previously called unclassified cardiomyopathy.

This diagnosis is used when the heart:

• Does not meet the criteria for HCM, RCM, DCM or ARVC

• Has features belonging to more than one phenotype

• Has regional areas of thickening and thinning

• Has impaired contraction without classic ventricular dilation

• Appears to be transitioning from one phenotype to another

• May represent an advanced or end-stage form of previous disease

Nonspecific cardiomyopathy is not one single disease. It is a category for abnormalities that cannot be placed confidently into another group.

Treatment is based on what the heart is actually doing, including:

• Whether congestive heart failure is present

• Whether contraction is reduced

• Whether the atria are enlarged

• Whether a clot is present

• Whether important arrhythmias are occurring

Can Cardiomyopathy Be Temporary?

Some cardiac changes that resemble primary cardiomyopathy can improve or resolve.

Transient myocardial thickening

Transient myocardial thickening can look almost identical to HCM at the first echocardiogram.

It has been reported after:

• Anaesthesia

• Surgery

• Trauma

• Pneumonia

• Severe inflammation

• Bite wounds

• Fever

• Toxoplasmosis

• Bartonella infection

• Other suspected causes of myocarditis

The thickening may represent myocardial oedema rather than true permanent hypertrophy.

A 2025 study evaluating serial echocardiograms found that a meaningful proportion of cats initially showing an HCM phenotype experienced subsequent reduction of the ventricular wall thickness.

Transient restrictive cardiomyopathy

As discussed above, some cats with acute heart failure and a restrictive phenotype later show normalisation of atrial size and ventricular filling.

Secondary ventricular thickening

Treating hypertension, hyperthyroidism or another underlying condition may allow some cardiac changes to improve.

This does not mean every thick or stiff heart will recover. Serial echocardiography is required to distinguish a transient process from persistent cardiomyopathy.

What Causes Cardiomyopathy in Cats?

The cause depends on the phenotype.

Primary myocardial disease

In many cats, the underlying cause is unknown. Genetic susceptibility is strongly suspected, particularly in HCM.

Secondary ventricular hypertrophy

A thickened ventricular wall may be caused or influenced by:

• Systemic hypertension

• Hyperthyroidism

• Acromegaly

• Aortic stenosis

• Reduced ventricular filling

• Infiltrative disease

Myocardial inflammation or injury

Myocarditis can cause:

• Temporary wall thickening

• Reduced ventricular contraction

• Abnormal rhythms

• Heart failure

• Mixed or nonspecific phenotypes

Potential triggers include infection, inflammation, toxins or immune-mediated injury, although a definitive cause is often not identified.

Nutritional deficiency

Taurine deficiency remains an important, potentially reversible cause of DCM, although it is uncommon in cats eating an appropriate complete diet.

Fibrosis

Fibrosis is a major feature of restrictive cardiomyopathy and may also develop within advanced HCM and other forms of myocardial disease.

What Are the Signs of Cardiomyopathy in Cats?

Many cats show no obvious signs during the early stages.

Cardiomyopathy may be discovered after a veterinarian detects:

• A heart murmur

• A gallop rhythm

• An irregular heartbeat

• An unusually rapid or slow heart rate

• An increased cardiac biomarker

• An abnormality before anaesthesia

• A family history of heart disease

When complications develop, the signs can appear suddenly.

Signs of Congestive Heart Failure

Possible signs include:

• Faster breathing while asleep

• Increased abdominal movement during breathing

• Difficulty settling or lying down

• Sitting upright with the elbows held away from the chest

• Extending the neck to breathe

• Open-mouth breathing

• Reduced appetite

• Lethargy

• Hiding

• Weakness

• Collapse

Cats with heart failure may develop pulmonary oedema, pleural effusion or both.

Coughing can occur, but it is less typical of feline heart failure than rapid or difficult breathing. A coughing cat also needs investigation for asthma, bronchitis, lungworm and other respiratory conditions.

Signs of Arterial Thromboembolism

A clot may form within an enlarged left atrium and then travel into an artery.

The classic presentation is feline aortic thromboembolism, also called FATE or a saddle thrombus.

Signs include:

• Sudden severe pain

• Crying or distress

• Sudden weakness or paralysis of one or both back legs

• Cold paws or limbs

• Pale, grey or blue footpads

• Weak or absent femoral pulses

• Rapid breathing

• Collapse

This is an immediate emergency.

Clopidogrel has been shown to reduce the risk of recurrent cardiogenic arterial thromboembolism more effectively than aspirin in cats that survived a previous event, although no medication eliminates the risk completely.

Signs of Right-Sided Heart Failure

Right-sided disease, particularly ARVC or advanced mixed cardiomyopathy, may cause:

• A swollen abdomen from ascites

• Pleural effusion

• Reduced appetite

• Weight loss

• Weakness

• Distended neck veins

• Liver congestion

• Difficulty breathing

Pleural effusion can occur with either left-sided or right-sided disease in cats.

Signs of an Abnormal Heart Rhythm

Arrhythmias may cause:

• Sudden weakness

• Fainting

• Brief collapse

• Reduced activity

• An unusually fast heartbeat

• An unusually slow heartbeat

• Sudden death

Some arrhythmias produce no visible signs and are discovered during an examination, ECG or longer Holter recording.

Does a Heart Murmur Mean a Cat Has Cardiomyopathy?

No.

A murmur is the sound of turbulent blood flow. It is not a diagnosis.

Cats may develop murmurs because of:

• HCM

• Dynamic ventricular outflow obstruction

• Congenital heart disease

• Hyperthyroidism

• Anaemia

• Fever

• Stress and increased cardiac output

• Pressure from the stethoscope or restraint

• Other cardiovascular conditions

In the CatScan study, 40.8% of apparently healthy cats had a murmur, but HCM was diagnosed in 14.7%. Many murmurs were therefore functional rather than caused by structural cardiomyopathy.

The opposite also applies: a cat can have cardiomyopathy without a murmur.

An echocardiogram is the most reliable way to determine whether structural heart disease is present.

How Worried Should You Be?

The ACVIM staging system applies to feline cardiomyopathy regardless of phenotype.

Stage	What it means	What to do
Stage A	The cat is at increased risk but has no current echocardiographic evidence of cardiomyopathy	Continue appropriate screening and routine health monitoring
Stage B1	Cardiomyopathy is present, but the cat has no symptoms and is at lower near-term risk of heart failure or thromboembolism	Follow the cardiologist’s recheck plan; routine medication may not be needed
Stage B2	The cat has no symptoms but has moderate or severe atrial enlargement or other findings indicating increased complication risk	Discuss clot prevention, closer monitoring and phenotype-specific treatment
Stage C	The cat currently has or has previously experienced heart failure or arterial thromboembolism	Ongoing cardiac medication and structured follow-up are required
Stage D	Heart failure is no longer controlled adequately with conventional stage C treatment	Specialist-directed escalation and quality-of-life planning are needed

A cat does not necessarily progress through every stage. Some remain in B1 throughout life. Others first present in stage C after developing acute heart failure or a saddle thrombus.

What Makes a Cat Higher Risk?

A ventricular wall measurement alone does not determine the full risk.

Features that increase concern include:

• Moderate or severe left atrial enlargement

• Progressive enlargement between examinations

• Reduced left atrial function

• Spontaneous echo contrast, which looks like smoke swirling within the atrium

• A visible intracardiac thrombus

• Marked ventricular hypertrophy

• Reduced ventricular contraction

• Regional wall thinning or abnormal movement

• A restrictive filling pattern

• A gallop rhythm

• Important arrhythmias

• Fainting

• Previous congestive heart failure

• Previous arterial thromboembolism

The left atrium often tells us more about immediate heart-failure and clot risk than the thickness of the ventricular wall alone.

When Is Cardiomyopathy an Emergency?

Go to an emergency veterinary hospital immediately if your cat develops:

• Open-mouth breathing

• Obvious breathing difficulty

• Strong abdominal effort during breathing

• An inability to lie down or settle

• Pale, blue or grey gums

• Sudden collapse

• Repeated fainting

• Sudden painful weakness or paralysis of one or more legs

• Cold hind paws

• Severe weakness

• Rapid deterioration over minutes or hours

Do not wait for a breathing rate to reach a particular number if the effort is clearly abnormal.

What should you do during a breathing emergency?

• Keep your cat calm and still.

• Place them in a well-ventilated carrier.

• Avoid unnecessary restraint.

• Call the emergency hospital while travelling.

• Do not force food, water or oral medication.

• Do not repeatedly remove the cat from the carrier to examine them.

• Give an additional diuretic only if your veterinarian has already provided a specific written emergency plan.

Stress can significantly worsen feline respiratory distress.

What should you do if the back legs suddenly stop working?

Treat this as an emergency even if you are unsure whether the cause is a clot, spinal injury or trauma.

Do not massage the limbs or apply direct heat. Keep your cat confined on soft bedding and travel immediately to an emergency veterinary hospital.

What Else Can Look Like Cardiomyopathy or Heart Failure?

Not every cat with rapid breathing, a murmur or an enlarged-looking heart has primary cardiomyopathy.

Important alternatives include:

Feline asthma or bronchitis

These conditions commonly cause coughing, wheezing and respiratory effort.

Pneumonia or lung infection

Fever, lethargy, inflammatory bloodwork and focal lung changes may increase suspicion.

Pleural disease

Pleural effusion may be caused by heart failure, cancer, pyothorax, chylothorax, bleeding or other conditions.

Anaemia

Severe anaemia can cause rapid breathing, weakness, pale gums and a flow murmur.

Hyperthyroidism

Hyperthyroidism can cause tachycardia, murmurs, hypertension and ventricular hypertrophy.

Systemic hypertension

High blood pressure can produce ventricular thickening and should be excluded before diagnosing primary HCM.

Acromegaly

Excess growth hormone can contribute to ventricular hypertrophy, often in cats with difficult-to-control diabetes.

Dehydration or reduced blood volume

A small ventricular chamber can make the heart walls appear falsely thickened.

Myocarditis

Inflammation or injury may cause wall thickening, systolic dysfunction, arrhythmias or a mixed cardiomyopathy phenotype.

Congenital heart disease

Valve abnormalities and abnormal communications between chambers or vessels can cause murmurs and cardiac enlargement.

Pericardial disease

Fluid or abnormal tissue around the heart can interfere with filling and mimic heart failure.

How Is Cardiomyopathy Diagnosed?

No single finding should be interpreted in isolation.

A proper investigation may include:

• Physical examination

• Echocardiography

• Blood-pressure measurement

• Thyroid testing

• Chest radiographs

• ECG

• NT-proBNP

• Cardiac troponin I

• Routine blood and urine testing

• Taurine testing

• Repeat imaging

Physical Examination

Your veterinarian will assess:

• Heart rate

• Heart rhythm

• Murmurs

• Gallop sounds

• Pulse quality

• Breathing rate and effort

• Gum colour

• Body condition

• Thyroid enlargement

• Blood pressure

• Evidence of fluid accumulation

• Limb pulses and temperature when a clot is suspected

A normal examination does not completely rule out cardiomyopathy.

Echocardiography

An echocardiogram is an ultrasound examination of the heart and is the main test for identifying the cardiomyopathy phenotype.

It allows assessment of:

• Ventricular wall thickness

• Ventricular chamber dimensions

• Ventricular contraction

• Relaxation and filling

• Left and right atrial size

• Valve movement

• Dynamic outflow obstruction

• Spontaneous echo contrast

• Intracardiac thrombi

• Congenital abnormalities

• Pleural or pericardial fluid

Echocardiography is also needed to stage the disease and guide medication choices.

A veterinary cardiologist is particularly valuable when:

• Measurements are borderline

• The phenotype is unclear

• A cat is intended for breeding

• A clot or spontaneous echo contrast is present

• Significant obstruction is suspected

• The cat has experienced heart failure, fainting or thromboembolism

• Treatment decisions are complex

Blood-Pressure Measurement

Blood pressure should be measured carefully with time allowed for acclimatisation.

Systemic hypertension can cause or worsen ventricular hypertrophy and commonly accompanies:

• Chronic kidney disease

• Hyperthyroidism

• Primary hypertension

• Some endocrine disorders

An unexpectedly high reading should usually be repeated because stress can increase blood pressure substantially in cats.

Thyroid Testing

Total thyroxine testing is particularly important in middle-aged and senior cats.

Hyperthyroidism can cause:

• Rapid heart rate

• Heart murmur

• High blood pressure

• Ventricular thickening

• Increased cardiac workload

• Weight loss despite a good appetite

Cardiac changes may improve when the hyperthyroidism and hypertension are controlled.

Chest X-Rays

Thoracic radiographs help assess:

• Pulmonary oedema

• Pleural effusion

• Heart silhouette

• Pulmonary blood vessels

• Airway disease

• Lung disease

• Other causes of respiratory distress

X-rays cannot reliably identify the cardiomyopathy phenotype. A cat can also have significant cardiomyopathy while the overall heart silhouette remains within normal limits.

A cat in severe respiratory distress may need oxygen, point-of-care ultrasound or thoracocentesis before conventional radiographs are attempted.

NT-proBNP Testing

NT-proBNP is released when cardiac muscle experiences increased stretch or pressure.

It can be useful for:

• Screening a cat with a murmur

• Supporting suspicion of moderate or severe occult heart disease

• Helping distinguish cardiac from non-cardiac respiratory distress

• Deciding whether echocardiography should be prioritised

It is not a definitive cardiomyopathy test.

A normal result may miss mild disease, while an increased result can occur with other cardiac and systemic conditions. In one multicentre study, a point-of-care NT-proBNP test was most useful for identifying moderate to severe occult heart disease rather than mild disease.

Cardiac Troponin I

Cardiac troponin I is released when heart-muscle cells are injured.

It may be increased with:

• Severe HCM

• Myocarditis

• Transient myocardial thickening

• Transient restrictive cardiomyopathy

• Myocardial ischaemia

• Systemic illness affecting the heart

Troponin supports clinical reasoning but does not identify one specific cardiomyopathy on its own.

A markedly increased result that falls as the echocardiographic abnormalities resolve can support suspicion of a transient inflammatory myocardial process.

Electrocardiography and Holter Monitoring

An ECG may be recommended when:

• An irregular rhythm is heard

• The heart rate is unusually fast or slow

• Fainting or collapse has occurred

• Atrial fibrillation is suspected

• Ventricular premature complexes are present

• Anti-arrhythmic treatment is being considered

A short ECG can miss intermittent arrhythmias. A Holter monitor or wearable ECG device may be needed when episodes occur unpredictably.

Blood and Urine Testing

Routine testing helps assess:

• Kidney function

• Liver values

• Electrolytes

• Anaemia

• Infection or inflammation

• Thyroid status

• Glucose

• Protein levels

• The cat’s ability to tolerate medication

Baseline kidney values and electrolytes are especially important before and after starting diuretics.

Taurine Testing

Whole-blood and plasma taurine should be considered when DCM is diagnosed, particularly when the diet is:

• Home prepared

• Nutritionally incomplete

• Unusual or highly restricted

• Not formulated specifically for cats

• Associated with possible ingredient or processing concerns

Treatment should not be delayed while waiting for results when deficiency is genuinely possible.

How Is Cardiomyopathy Treated?

There is no universal cardiac medication plan for every cat.

Treatment is based on:

• Phenotype

• Disease stage

• Atrial size

• Systolic function

• Presence of outflow obstruction

• Blood-clot risk

• Heart rhythm

• Kidney function

• Blood pressure

• Current or previous heart failure

Treatment for Stage A

Stage A cats have increased risk but no current evidence of cardiomyopathy.

Management may include:

• Periodic veterinary examinations

• Echocardiographic screening for predisposed breeds

• Breed-appropriate genetic testing

• Blood-pressure monitoring

• Thyroid testing as the cat ages

• Maintaining a healthy body condition

Routine cardiac medication is not indicated solely because a cat belongs to an at-risk breed.

Treatment for Stage B1

Most stage B1 cats require monitoring rather than automatic medication.

Depending on the findings, the recheck interval may be approximately 6 to 12 months. Borderline or changing abnormalities may justify earlier reassessment.

A beta blocker such as atenolol may be considered when there is:

• Severe dynamic left ventricular outflow obstruction

• A clinically important tachyarrhythmia

• Another specific cardiology indication

Beta blockers and calcium-channel blockers are not routine medication for every asymptomatic cat with cardiomyopathy.

Delayed-Release Sirolimus for Subclinical HCM

In the United States, delayed-release sirolimus received conditional FDA approval in March 2025 for managing ventricular hypertrophy in carefully selected cats with subclinical HCM.

Eligible cats must not have:

• Current or previous congestive heart failure

• Current or previous arterial thromboembolism

• Severe left ventricular outflow obstruction

• Another cause of ventricular hypertrophy

• Pre-existing liver disease

• Diabetes mellitus

The medication is intended specifically for eligible subclinical HCM. It is not approved as a treatment for RCM, DCM, ARVC, nonspecific cardiomyopathy or acute heart failure.

Conditional approval means there is a reasonable expectation of effectiveness while further evidence is being collected.

The available evidence supports an effect on ventricular wall thickness. It has not yet established that the medication prevents:

• Congestive heart failure

• Arterial thromboembolism

• Sudden death

• Cardiovascular death

• Reduced overall survival

Eligibility and monitoring should be determined by a veterinarian experienced in feline cardiology.

Treatment for Stage B2

Stage B2 cats are symptom-free but have a greater risk of heart failure or arterial thromboembolism.

Treatment may include antithrombotic medication when there is:

• Moderate or severe left atrial enlargement

• Reduced atrial function

• Spontaneous echo contrast

• A visible intracardiac thrombus

• Very slow left atrial appendage flow

• Another important clot-risk finding

Clopidogrel is commonly used. Rivaroxaban or combination treatment may be considered in selected very high-risk cats.

Not every stage B2 cat needs the same medication. Treatment burden, bleeding risk and the cat’s ability to take tablets must be considered alongside the echocardiographic findings.

Treatment for Acute Congestive Heart Failure

Emergency treatment may include:

• Minimal handling

• Oxygen support when tolerated

• Injectable furosemide

• Thoracocentesis for significant pleural effusion

• Careful sedation to reduce panic

• Temperature support

• Blood-pressure monitoring

• ECG monitoring

• Treatment of an important arrhythmia

Furosemide is the principal medication used to remove fluid associated with feline heart failure.

Thoracocentesis may provide faster relief than diuretics when a large amount of pleural fluid is physically preventing the lungs from expanding.

Intravenous fluids must be used cautiously. A cat may need circulatory support, but excessive fluid can worsen pulmonary oedema or pleural effusion.

Treatment for Chronic Heart Failure

Once the cat is stable, treatment may include:

• Oral furosemide

• Antithrombotic medication when clot risk is significant

• Potassium supplementation when required

• Additional cardiac medication selected from the echocardiogram

• Regular kidney and electrolyte monitoring

• Home respiratory-rate monitoring

Pimobendan may be considered in selected cats with reduced ventricular systolic function or low cardiac output when clinically important dynamic outflow obstruction is absent.

A retrospective study found that pimobendan appeared reasonably well tolerated in cats with heart failure and ventricular systolic dysfunction, although it is not appropriate for every feline cardiac phenotype.

ACE inhibitors and spironolactone may be used in selected patients but are not universal requirements for every cat with cardiomyopathy.

Treatment for Stage D Heart Failure

Stage D means conventional treatment is no longer controlling the heart failure adequately.

Specialist-directed options may include:

• Adjustment of loop-diuretic treatment

• Alternative diuretics

• Additional neurohormonal medication

• Pimobendan in suitable haemodynamic conditions

• More frequent drainage of recurrent pleural fluid

• Oxygen during decompensation

• Nutritional and appetite support

• Palliative treatment focused on comfort

The goal is to balance fluid control against:

• Dehydration

• Kidney injury

• Electrolyte abnormalities

• Low blood pressure

• Medication stress

• Reduced appetite

Treatment for Dilated Cardiomyopathy

DCM treatment may include:

• Taurine supplementation when deficiency is possible

• Immediate correction of an incomplete diet

• Furosemide for congestive heart failure

• Pimobendan for reduced systolic function where appropriate

• Antithrombotic medication when the left atrium is enlarged

• Treatment of important arrhythmias

• Careful nutritional support

Cardiac improvement from taurine supplementation takes time. Medication for heart failure should not be stopped until serial examinations show that it is safe to do so.

Treatment for Restrictive Cardiomyopathy

There is no medication that reliably removes established myocardial fibrosis.

Treatment focuses on:

• Controlling pulmonary oedema or pleural effusion

• Reducing arterial thromboembolism risk

• Treating clinically important arrhythmias

• Monitoring atrial enlargement

• Maintaining kidney function and appetite

• Repeating echocardiography when a transient phenotype is possible

A younger cat with an acute antecedent event may need serial imaging before permanent RCM is assumed.

Treatment for Arrhythmogenic Right Ventricular Cardiomyopathy

Treatment may include:

• Diuretics

• Thoracocentesis

• Abdominocentesis for uncomfortable ascites

• Pimobendan when systolic dysfunction is present and treatment is considered appropriate

• Anti-arrhythmic medication based on ECG or Holter findings

• Blood-pressure and kidney monitoring

• Antithrombotic medication when atrial enlargement creates clot risk

The rarity of feline ARVC means treatment evidence is limited and specialist guidance is particularly valuable.

Treatment for Arterial Thromboembolism

An acute arterial thromboembolism requires:

• Strong opioid pain relief

• Antithrombotic medication

• Treatment of concurrent heart failure

• Monitoring of potassium and kidney function

• Temperature support

• Nursing care for immobile limbs

• Monitoring for reperfusion injury

• A realistic discussion of recovery and quality of life

Clot-dissolving treatment and surgical thrombectomy may be available at selected specialty hospitals, but neither is a guaranteed treatment and both require intensive monitoring.

How Do You Monitor a Cat With Cardiomyopathy at Home?

The most useful home measurement is usually the sleeping respiratory rate.

How to Count the Sleeping Respiratory Rate

1. Wait until your cat is deeply asleep and not purring.

2. Watch the chest or abdomen.

3. One complete rise and fall equals one breath.

4. Count for 30 seconds.

5. Multiply the number by two.

6. Record the result.

Count under similar conditions each time.

Most healthy cats and cats with stable, medically controlled heart failure have an average sleeping respiratory rate below 30 breaths per minute. A repeated increase above the cat’s normal baseline deserves attention.

When should you call the vet?

Contact your veterinary team when:

• Several genuine sleeping measurements exceed 30 breaths per minute

• The rate is consistently rising from the normal baseline

• Appetite has fallen

• Your cat is hiding or unusually weak

• Medication is being vomited or cannot be given

• Body weight changes quickly

• Water intake or urination changes significantly

• Fainting or collapse occurs

When is breathing urgent?

Seek urgent or emergency care for:

• A sleeping or resting rate above approximately 40 breaths per minute

• Increased abdominal effort

• An inability to settle

• Open-mouth breathing

• Pale, blue or grey gums

• Collapse

Breathing effort matters more than obtaining a perfect number.

What Else Should You Monitor?

Keep a simple record of:

• Sleeping respiratory rate

• Appetite

• Body weight

• Energy

• Social behaviour

• Hiding

• Vomiting

• Water intake

• Urination

• Medication doses

• Fainting episodes

• Hind-limb strength and temperature

• Difficulty administering tablets

A trend is usually more informative than one isolated measurement.

What Should You Do If Your Vet Finds a Heart Murmur?

Do not panic, but do not treat the murmur as a diagnosis.

1. Ask whether anything else was heard

Find out whether the veterinarian detected:

• A gallop sound

• An arrhythmia

• A very rapid heart rate

• Abnormal pulse quality

2. Consider the cat’s risk factors

These include:

• Breed

• Family history

• Age

• Known genetic variant

• Fainting

• Abnormal breathing

• Planned breeding

• Previous unexplained collapse

3. Check for secondary causes

Blood pressure and thyroid testing may be needed, particularly in an older cat.

4. Arrange echocardiography

An echocardiogram determines whether structural disease is present and identifies the phenotype.

5. Do not start random heart medication

A medication that helps one type or stage of cardiomyopathy may be unnecessary or harmful in another.

What Should You Ask After a Cardiomyopathy Diagnosis?

Ask your veterinary or cardiology team:

• What phenotype does my cat have?

• What stage is the disease?

• Is the left atrium enlarged?

• Is atrial function reduced?

• Is spontaneous echo contrast present?

• Is there a visible clot?

• Is ventricular contraction normal?

• Is outflow obstruction present?

• Is my cat currently in heart failure?

• Does my cat need clopidogrel or another antithrombotic?

• What sleeping respiratory rate should trigger a phone call?

• When should the echocardiogram be repeated?

• What should I do during a breathing emergency?

• Does the anaesthetic or fluid plan need to change?

• Could this be a transient or secondary phenotype?

A report containing only the words “cardiomyopathy” or “thickened heart” is not enough to make the best long-term decisions.

Common Mistakes Owners Make

Assuming every murmur means cardiomyopathy

Many cats have functional murmurs. An echocardiogram is needed to identify structural disease.

Assuming no murmur means the heart is normal

Some cats with significant cardiomyopathy have no detectable murmur.

Focusing only on ventricular wall thickness

The left atrium, clot risk, systolic function, heart rhythm and disease stage often matter more clinically.

Waiting for a cough

Cats in heart failure more commonly develop rapid or difficult breathing than a classic cardiac cough.

Adjusting furosemide without a plan

Too little may fail to control fluid. Too much may contribute to dehydration, kidney injury and electrolyte abnormalities.

Assuming taurine cures every case of DCM

Taurine helps when deficiency caused the disease. Modern feline DCM is frequently unrelated to taurine deficiency.

Assuming a negative genetic result clears a cat of HCM

Available DNA tests identify only specific variants. Echocardiographic screening is still required.

Stopping medication when the cat looks better

Heart failure may return rapidly when medication is reduced or stopped without reassessment.

Should Cats With Cardiomyopathy Be Bred?

A cat with echocardiographically confirmed primary cardiomyopathy should generally not be used for breeding.

For HCM, routine genetic testing currently has the strongest support for:

• A31P in Maine Coon cats

• R818W in Ragdoll cats

Cats with two copies of a recognised pathogenic variant carry greater concern and should not be bred.

Management of a cat with one copy can be more complicated in small breeding populations because removing every carrier immediately may reduce genetic diversity. Any breeding decision should involve:

• Echocardiographic screening

• DNA testing

• Pedigree analysis

• A negative breeding partner if breeding is retained temporarily

• Avoidance of producing homozygous kittens

• Ongoing screening of offspring

• Removal of clinically affected cats from breeding

A veterinary cardiologist and geneticist familiar with the breed should guide the programme.

Can Cardiomyopathy Be Prevented?

Most primary feline cardiomyopathies cannot currently be prevented in an individual cat.

Practical risk reduction includes:

• Feeding a complete, balanced feline diet with adequate taurine

• Avoiding nutritionally incomplete home-prepared diets

• Maintaining a healthy body condition

• Screening cats from predisposed breeds

• Investigating persistent murmurs, gallops and arrhythmias

• Measuring blood pressure

• Testing older cats for hyperthyroidism

• Treating hypertension and endocrine disease

• Informing veterinarians of known heart disease before anaesthesia or fluid therapy

• Following the cardiologist’s recheck schedule

• Monitoring breathing at home

• Avoiding breeding clinically affected cats

No supplement has been proven to prevent primary HCM, RCM or ARVC.

Extreme salt restriction should not be started without veterinary advice. Maintaining a complete, palatable diet and adequate food intake is particularly important in cats with chronic heart disease.

Can a Cat With Cardiomyopathy Have Anaesthesia?

Yes, when the procedure is necessary and the risk is assessed carefully.

Cardiomyopathy does not automatically mean that a cat can never receive:

• General anaesthesia

• Sedation

• Dental treatment

• Surgery

• Intravenous fluid therapy

The plan may need adjustment based on:

• Disease stage

• Left atrial size

• Current heart failure

• Outflow obstruction

• Blood pressure

• Heart rhythm

• Kidney function

• Medication

• The urgency of the procedure

A stable stage B1 cat and a cat with recent congestive heart failure have very different anaesthetic risks.

The anaesthetist should know about the heart disease before the procedure begins.

What Is the Prognosis?

There is no single life expectancy for feline cardiomyopathy.

The prognosis depends more on the stage and complications than on the name of the phenotype alone.

Hypertrophic Cardiomyopathy Prognosis

Many cats with mild or moderate subclinical HCM remain stable for years and may never develop clinical complications.

In the REVEAL study of more than 1,000 cats with preclinical HCM or obstructive HCM:

• 30.5% developed congestive heart failure, arterial thromboembolism or both during the study period.

• 27.9% experienced cardiovascular death.

• A minority remained exceptionally long-lived, with 10% reaching 9 to 15 years after study entry.

These results describe a large population and cannot predict the exact future of one cat.

Restrictive Cardiomyopathy Prognosis

RCM generally has a more guarded prognosis than mild HCM because many cats already have substantial atrial enlargement or heart failure when diagnosed.

In one 92-cat study, the median cardiac survival for cats with the myocardial form and available follow-up was 667 days. Severe left atrial enlargement was associated with a shorter outcome.

Cats with transient restrictive cardiomyopathy may have a much better prognosis once the phenotype resolves, which is why serial imaging matters in appropriate cases.

Dilated Cardiomyopathy Prognosis

Taurine-deficient DCM may improve substantially with supplementation and diet correction.

Non-taurine DCM has a more guarded prognosis, especially when the cat presents with:

• Severe systolic dysfunction

• Heart failure

• Low blood pressure

• Arrhythmias

• Marked atrial enlargement

• Arterial thromboembolism

Arrhythmogenic Right Ventricular Cardiomyopathy Prognosis

Evidence is limited because feline ARVC is rare.

The outlook is generally guarded when the cat has:

• Severe right-sided chamber enlargement

• Recurrent ascites or pleural effusion

• Ventricular arrhythmias

• Fainting

• Reduced left ventricular function

• Refractory heart failure

Nonspecific Cardiomyopathy Prognosis

The prognosis depends on the abnormalities that placed the cat in this category.

A nonspecific phenotype with mild stable changes may behave very differently from one representing end-stage myocardial disease with poor contraction and major atrial enlargement.

What Findings Matter Most for Prognosis?

Across phenotypes, greater concern is associated with:

• Moderate or severe atrial enlargement

• Progressive enlargement

• Reduced atrial function

• Spontaneous echo contrast

• An intracardiac thrombus

• Previous arterial thromboembolism

• Congestive heart failure

• Reduced ventricular contraction

• Important arrhythmias

• Fainting

• Poor kidney function

• Loss of appetite or body weight

• Poor response to treatment

The cat’s response to treatment and quality of life are more useful than treating one published survival statistic as a countdown.

Will My Cat Be Okay?

Many cats with cardiomyopathy remain comfortable for a long time.

A stage B1 diagnosis does not mean that heart failure is imminent. It means that the heart should be monitored so progression can be recognised.

Stage B2 carries greater risk, but identifying the stage allows the veterinary team to consider clot prevention and closer monitoring before a crisis occurs.

Cats that develop heart failure, arterial thromboembolism or serious arrhythmias have a more guarded outlook. Even then, some respond well and regain a good quality of life.

The goals of treatment are to keep your cat:

• Breathing comfortably

• Eating

• Maintaining weight

• Moving normally

• Interacting with the family

• Free from repeated distress

• Receiving medication without an excessive treatment burden

Frequently Asked Questions

Can a cat with cardiomyopathy live a normal lifespan?

Yes. Some cats with mild, stable, subclinical cardiomyopathy live a normal or near-normal lifespan. The prognosis becomes more guarded when atrial enlargement, heart failure, arterial thromboembolism, fainting or important arrhythmias develop.

Can feline cardiomyopathy be cured?

Most primary cardiomyopathies cannot be cured. Taurine-deficient DCM, transient myocardial thickening and transient restrictive cardiomyopathy may improve or resolve when the underlying process is corrected or settles.

Does a heart murmur mean my cat has heart disease?

No. Cats can have functional murmurs without structural heart disease, and cats with cardiomyopathy may have no murmur. Echocardiography is needed to determine whether cardiomyopathy is present.

Is rapid breathing always caused by heart failure?

No. Asthma, pneumonia, pleural disease, pain, fever, anaemia and other conditions can also increase breathing. A cat with rapid or laboured breathing needs examination rather than an automatic extra dose of heart medication.

Can a cat with cardiomyopathy safely have surgery or a dental procedure?

Often, yes. The risk depends on the phenotype, stage, atrial size, heart rhythm, blood pressure and whether heart failure has occurred. The anaesthetic and fluid plan should be tailored to the individual cat.

Final Thoughts

Cardiomyopathy is an umbrella term rather than one diagnosis.

Hypertrophic cardiomyopathy is the most common type, but restrictive, dilated, arrhythmogenic right ventricular and nonspecific phenotypes also occur. Some secondary and transient conditions can closely imitate primary cardiomyopathy.

The most useful information is not simply whether the heart is thick, stiff or weak. What matters most is:

• The cardiomyopathy phenotype

• The disease stage

• Left and right atrial size

• Systolic function

• Heart rhythm

• Blood-clot risk

• Whether heart failure has developed

An incidental murmur in a comfortable cat is not usually an emergency, but it deserves appropriate investigation. Open-mouth breathing, marked respiratory effort, collapse or sudden painful limb paralysis requires immediate care.

Many cats remain stable for years. The safest approach is accurate diagnosis, stage-based treatment and careful monitoring rather than panic, complacency or one medication plan applied to every heart.

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If you are unsure whether your cat’s murmur, breathing pattern or echocardiogram findings are urgent, ASK A VET™ can help you understand the warning signs and prepare the right questions for your veterinary or cardiology team.