Is a Heart Murmur in a Horse Serious?

By Dr Duncan Houston

Hearing that your horse has a heart murmur can be alarming, especially when the horse is older, competing or expected to carry a rider at speed.

The reassuring reality is that heart murmurs are common in horses, particularly fit athletic horses, and many do not affect health, performance or lifespan. Others indicate valve disease, a congenital defect or an infection that needs careful investigation.

What matters most is not simply how loud the murmur sounds. The real concern is whether the heart is enlarging, whether the rhythm is becoming unstable, whether the horse’s performance is changing and whether there is any risk of collapse.

Quick Answer

A heart murmur is an extra sound caused by turbulent or high-velocity blood flow. Some soft, brief murmurs are physiologic and occur in completely healthy horses.

A new, changing, moderate-to-loud, holosystolic or diastolic murmur usually warrants further assessment, particularly if the horse has poor performance, an abnormal pulse, an irregular rhythm, breathing difficulty or collapse. Many horses with mild valve leakage can continue working normally, while severe valve disease, pulmonary hypertension, heart failure or complex ventricular arrhythmias may make riding unsafe. (Tierspital Zürich)

Heart Murmurs in Horses at a Glance

Finding	Common interpretation	Typical next step
Brief grade 1–2 systolic murmur at the left heart base	Often a physiologic flow murmur	Record and monitor
Early diastolic squeak in a young, fit horse	May be a physiologic filling murmur	Monitor if the examination is otherwise normal
Systolic murmur loudest over the left apex	Possible mitral regurgitation	Echocardiography depending on grade and pattern
Diastolic murmur over the left heart base	Aortic regurgitation is likely	Echocardiography is generally recommended
Systolic murmur over the right side	Often tricuspid regurgitation, sometimes training-related	Assess grade, performance and chamber size
Loud right-sided systolic murmur in a young horse	Ventricular septal defect must be considered	Echocardiography
Continuous murmur in a foal	Patent ductus arteriosus or another congenital lesion	Prompt echocardiography if persistent
Murmur with fever or weight loss	Infective endocarditis is a concern	Urgent investigation
Murmur with collapse or complex arrhythmia	Potential safety risk	Stop work and obtain urgent cardiac assessment

The timing, location, duration and shape of the murmur are usually more informative than the grade by itself. (Tierspital Zürich)

What Is a Heart Murmur?

A normal equine heartbeat contains several heart sounds created by valve closure, blood movement and cardiac filling. A murmur is an additional sound produced when blood flow becomes sufficiently turbulent or unusually fast.

That turbulence may result from:

• Normal high-volume blood flow in a fit horse

• Blood leaking backwards through a valve

• Blood passing through a congenital opening

• Blood being forced through a narrowed outflow tract

• Anaemia, fever, colic or another condition increasing circulation

• Structural heart disease

A murmur describes a sound. It does not provide the complete diagnosis.

How Are Heart Murmurs Graded?

Veterinarians commonly use a six-point scale:

Grade	Description
1/6	Very soft and heard only in a quiet environment after careful listening
2/6	Soft but heard as soon as the stethoscope is placed correctly
3/6	Moderately loud with some radiation
4/6	Very loud and heard over a wider area
5/6	Very loud with a palpable vibration called a thrill
6/6	Audible with the stethoscope held slightly away from the chest, with a palpable thrill

The grade describes loudness, not the amount of heart damage. Musical murmurs can sound striking despite relatively limited regurgitation, while severe heart failure may sometimes produce a quieter murmur because forward blood flow has fallen. (Large Animal Hospital)

Are Heart Murmurs Common in Horses?

Yes.

Both physiologic murmurs and murmurs associated with valve leakage are common in equine athletes. Doppler ultrasound may also detect mild valve regurgitation in horses that have no audible murmur and no evidence of heart disease.

Soft murmurs frequently have no effect on performance or health. The clinical challenge is deciding which sound represents normal equine circulation and which represents a lesion that may progress. (Tierspital Zürich)

A murmur may also become temporarily louder when a horse:

• Exercises

• Has a fever

• Is anaemic

• Is in pain

• Has colic

• Is dehydrated

• Has increased cardiac output for another reason

These functional murmurs may lessen or disappear when the underlying condition resolves. (IVIS)

How Does a Veterinarian Describe a Murmur?

A useful murmur description includes more than the grade.

Timing

A murmur may be:

• Systolic: heard while the ventricles contract

• Diastolic: heard while the ventricles relax and fill

• Continuous: heard through both phases

A systolic murmur generally occurs with the arterial pulse. A diastolic murmur is heard in the interval between pulses. (Large Animal Hospital)

Point of Maximum Intensity

This is the place on the chest where the murmur sounds loudest.

It helps identify which valve or structure may be involved:

• Left apex: mitral valve

• Left base: aortic or pulmonic valve

• Right side: tricuspid valve or ventricular septum

Duration

A murmur may occupy:

• Early systole

• Mid-systole

• Late systole

• All of systole

• Part or all of diastole

A brief early-to-mid-systolic murmur is more consistent with physiologic outflow. A holosystolic or pansystolic murmur is more suspicious for mitral or tricuspid regurgitation or a ventricular septal defect.

Shape and Character

Murmurs may sound:

• Blowing

• Musical

• Buzzing

• Honking

• Crescendo

• Decrescendo

• Plateau-shaped

Aortic regurgitation often creates a musical, buzzing or decrescendo diastolic murmur. Mitral regurgitation is more commonly a blowing, plateau-shaped systolic murmur. (IVIS)

Which Heart Murmurs Can Be Normal?

Physiologic Systolic Flow Murmurs

A physiologic flow murmur is commonly:

• Grade 1–3/6

• Brief

• Early to mid-systolic

• Loudest over the left heart base

• Localised rather than widely radiating

• Present without chamber enlargement, arrhythmia or poor performance

It reflects high-volume blood flow through a structurally normal heart rather than defective valve closure. These murmurs are particularly common in fit horses. (Tierspital Zürich)

Physiologic Diastolic Filling Murmurs

Young and athletic horses may have a brief, soft, squeaking murmur during rapid ventricular filling.

This should not be confused with the longer decrescendo diastolic murmur of aortic regurgitation. A physiologic filling murmur is generally short, low-grade and heard around the cardiac apex. (Tierspital Zürich)

Mild Training-Associated Valve Regurgitation

Mild mitral or tricuspid regurgitation can develop or become more detectable with athletic training.

Training-associated tricuspid regurgitation is particularly common in performance horses and may be clinically insignificant when:

• The valve looks normal

• The right atrium and ventricle remain normal in size

• There is no pulmonary hypertension

• The horse performs normally

• The murmur remains stable

A loud right-sided murmur, poor performance or right-heart enlargement changes that interpretation. (Tierspital Zürich)

What Causes Aortic Regurgitation in Horses?

Aortic regurgitation occurs when the aortic valve does not close completely and blood leaks from the aorta back into the left ventricle during diastole.

It is a common finding in older horses and is often caused by age-related thickening, degeneration, redundancy or prolapse of the aortic valve. Less common causes include congenital abnormalities, torn valve tissue, infective endocarditis and disease of the aortic root. (Tierspital Zürich)

What Does the Murmur Sound Like?

The murmur is usually:

• Diastolic

• Loudest over the left aortic valve area

• Decrescendo

• Blowing, musical, buzzing or honking

• Sometimes audible on the right side as it becomes louder

A buzzing or musical quality does not automatically mean severe disease. Valve vibration can produce a dramatic sound with a relatively small regurgitant flow. (Merck Veterinary Manual)

Is Aortic Regurgitation Always Serious?

No.

Mild aortic regurgitation in an older horse is often discovered incidentally and may remain stable for years without affecting work or life expectancy.

Concern increases when:

• It is moderate or severe

• It is first recognised in a horse younger than ten

• The left ventricle is enlarging

• The pulse is strongly bounding

• The difference between systolic and diastolic blood pressure is widening

• The aortic root is enlarging

• Secondary mitral regurgitation develops

• Atrial fibrillation occurs

• Ventricular premature beats appear at rest or during exercise

Moderate-to-severe aortic regurgitation has been associated with ventricular arrhythmias and rare sudden cardiac death, sometimes without a previous history of heart failure or obvious poor performance. (Tierspital Zürich)

What Causes Mitral Regurgitation in Horses?

Mitral regurgitation occurs when blood leaks from the left ventricle back into the left atrium during systole.

Possible causes include:

• Mild functional regurgitation

• Age-related valve degeneration

• Mitral valve prolapse

• Congenital valve abnormalities

• Rupture of the chordae tendineae

• Infective endocarditis

• Papillary muscle dysfunction

The murmur is usually systolic and loudest over the left cardiac apex. It may occupy the middle or later part of systole or continue throughout systole. (Tierspital Zürich)

When Is Mitral Regurgitation Concerning?

Mild mitral regurgitation without cardiac enlargement often has a favourable prognosis and may not affect performance.

More concerning findings include:

• Moderate-to-severe regurgitation

• Progressive left atrial enlargement

• Left ventricular volume overload

• Pulmonary artery enlargement

• Pulmonary hypertension

• Atrial fibrillation or persistent tachycardia

• Markedly thickened valve tissue

• A flail valve leaflet

• Ruptured chordae tendineae

• Infective endocarditis

• Reduced ventricular function

Left atrial enlargement is particularly important because it increases the risk of atrial fibrillation. (Tierspital Zürich)

Can Mitral Regurgitation Cause Heart Failure?

Severe mitral regurgitation may eventually increase pressure within the pulmonary circulation and contribute to left-sided congestive heart failure.

Warning signs can include:

• Rapid or laboured breathing at rest

• Reduced exercise tolerance

• Persistent tachycardia

• Pulmonary crackles

• Severe weakness

• Pulmonary oedema

• Frothy fluid at the nostrils in advanced cases

Heart failure remains uncommon compared with mild incidental valve leakage, but respiratory distress in a horse with a known murmur is an emergency. (Merck Veterinary Manual)

What Does a Tricuspid Murmur Mean?

Tricuspid regurgitation allows blood to leak from the right ventricle into the right atrium during systole.

It is commonly detected in athletic horses and may be an adaptation associated with age and training rather than progressive disease.

The finding becomes more concerning when accompanied by:

• A grade 4–6/6 murmur

• Right atrial or right ventricular enlargement

• Structural damage to the valve

• Pulmonary hypertension

• Severe respiratory disease

• Jugular distension

• Ventral oedema

• Atrial fibrillation

• Right-sided heart failure

Tricuspid valve infection can also occur, particularly in association with septic jugular thrombophlebitis, although this is uncommon. (Tierspital Zürich)

What Do Heart Murmurs Mean in Foals?

Murmurs are not unusual during the transition from fetal to newborn circulation. A brief, soft murmur may disappear as the cardiovascular system adapts after birth.

A persistent, loud or continuous murmur requires closer investigation because congenital defects may be present.

Ventricular Septal Defect

A ventricular septal defect is an opening between the left and right ventricles and is the most commonly recognised congenital cardiac defect in horses.

The murmur is usually:

• Systolic

• Loud

• Blowing

• Most obvious on the right side

• Sometimes audible over the left pulmonic area

The importance of the defect depends on its size, location, pressure gradient and effect on heart-chamber size. Some small defects permit a normal athletic life, while large or complex defects may cause poor growth, exercise intolerance, cyanosis or heart failure. (PubMed Central (PMC))

Patent Ductus Arteriosus

The ductus arteriosus is a normal fetal blood vessel that should close after birth.

A continuous murmur may be heard temporarily in a very young foal during normal closure. A persistent continuous murmur or an unwell foal requires echocardiography to determine whether the vessel remains open or another congenital abnormality is present. (Large Animal Hospital)

Could a New Murmur Mean Heart Infection?

Yes.

Infective endocarditis is an uncommon but life-threatening infection of the heart valves.

Warning signs may include:

• Persistent or recurring fever

• A new or changing murmur

• Depression

• Poor appetite

• Weight loss

• Tachycardia

• Arrhythmia

• Lameness or signs of septic embolisation

• Jugular thrombophlebitis

• Heart failure

The mitral and aortic valves are affected most often. Diagnosis commonly involves blood cultures and echocardiography. A new murmur in a horse with persistent fever should never be dismissed as age-related valve disease without further investigation. (PubMed Central (PMC))

Does Murmur Grade Tell You How Serious It Is?

Not reliably.

A grade 1 murmur is not automatically harmless, and a grade 4 musical murmur is not automatically severe. The murmur must be interpreted alongside:

• Timing

• Duration

• Location

• Character

• Horse’s age

• Whether it is new or changing

• Pulse quality

• Heart rhythm

• Exercise history

• Echocardiographic chamber size

• Ventricular function

• Pulmonary pressure

• Intended use of the horse

The absence of heart-chamber enlargement makes chronic severe regurgitation much less likely, even when a colour Doppler jet looks striking. Serial examinations are often more useful for prognosis than one isolated scan. (Tierspital Zürich)

How Worried Should You Be?

Lower Risk

The horse has:

• A soft, brief early systolic murmur

• Normal heart rhythm

• Normal arterial pulses

• Normal performance

• Normal recovery after exercise

• No chamber enlargement

• No change on repeat examinations

What it likely means: A physiologic flow murmur or mild stable regurgitation is more likely.

What to do: Record the finding and follow your veterinarian’s monitoring schedule.

Moderate Concern

The horse has:

• A grade 3 murmur

• A persistent diastolic murmur

• A newly recognised murmur in an older horse

• Mild valve leakage without substantial enlargement

• No collapse or respiratory signs

• Normal or only mildly altered performance

What it may mean: Structural valve disease may be present but could still be well tolerated.

What to do: Arrange echocardiography, particularly before demanding competition, purchase, breeding or a major increase in workload.

High Concern

The horse has:

• Moderate-to-severe mitral or aortic regurgitation

• A murmur becoming louder on serial examinations

• Bounding arterial pulses

• An irregular rhythm

• Persistent resting tachycardia

• Poor exercise recovery

• Reduced performance

• Progressive chamber enlargement

• Pulmonary hypertension

• Exercise-induced ventricular premature beats

What it may mean: The lesion is affecting cardiac function or electrical stability.

What to do: Stop strenuous work until a cardiology assessment, echocardiogram and appropriate ECG testing have been completed.

Critical

The horse has:

• Collapse or fainting

• Severe weakness

• Breathing difficulty at rest

• Frothy nasal discharge

• Ventral, limb or brisket oedema

• A complex ventricular arrhythmia

• Pulmonary hypertension

• Congestive heart failure

• Fever with a new murmur

• Sudden deterioration during exercise

What it may mean: Advanced structural disease, a dangerous arrhythmia, endocarditis or heart failure may be present.

What to do: Treat this as an emergency and obtain immediate hands-on veterinary care.

When Is This an Emergency?

Contact an equine veterinarian immediately if a horse with a murmur develops:

• Collapse

• Syncope or apparent fainting

• Severe exercise intolerance

• Staggering or weakness during work

• Rapid or laboured breathing at rest

• Frothy nasal discharge

• Persistent resting tachycardia

• A markedly irregular rhythm

• Pale, grey or blue mucous membranes

• Ventral or limb oedema

• Distended jugular veins

• Recurrent fever

• Sudden poor performance

• Signs of heart failure

Horses with pulmonary hypertension, congestive heart failure or complex ventricular arrhythmias are considered unsafe to ride or drive. (Tierspital Zürich)

What To Do Right Now After a Murmur Is Found

1. Ask for the Complete Description

Record:

• Grade

• Timing

• Location

• Duration

• Character

• Whether the rhythm was normal

• Whether the pulse was bounding, weak or irregular

• Whether the murmur has been documented before

“Has a murmur” is not enough information for meaningful long-term monitoring.

2. Review the Horse’s History

Tell your veterinarian about:

• Poor performance

• Slower recovery

• Coughing

• Abnormal breathing

• Weakness

• Collapse

• Recent fever

• Weight loss

• Previous severe infection

• Jugular catheter complications

• Current medications and supplements

• Expected athletic use

3. Avoid Strenuous Exercise When the Finding Is Concerning

A new moderate-to-loud murmur, left-sided diastolic murmur, abnormal pulse, arrhythmia or history of collapse should be investigated before demanding exercise continues.

Do not gallop or jump a horse to see whether the murmur matters. Exercise testing should be performed only after the resting examination has established that it is safe. (Tierspital Zürich)

4. Arrange Echocardiography When Indicated

A consensus panel recommends echocardiography for situations including:

• A previously functional murmur becoming louder

• Grade 3–6 left-sided murmurs compatible with mitral or aortic regurgitation

• Grade 4–6 right-sided murmurs compatible with tricuspid regurgitation

• Suspected congenital disease

• Continuous or combined systolic-diastolic murmurs

• Clinically important arrhythmias

• Suspected myocardial injury

• Suspected heart failure

Echocardiography may also be appropriate for lower-grade murmurs during a prepurchase examination when the result could affect the buyer’s decision. (Tierspital Zürich)

How Do Veterinarians Investigate a Murmur?

Full Cardiovascular Examination

The veterinarian evaluates:

• Heart rate

• Heart rhythm

• All valve areas on both sides

• Arterial pulse quality

• Mucous membranes

• Capillary refill

• Jugular filling and pulsation

• Limb and ventral oedema

• Lung sounds

• Exercise history

Echocardiography

A complete equine echocardiogram may use:

• Two-dimensional ultrasound

• M-mode imaging

• Colour Doppler

• Spectral Doppler

It evaluates:

• Valve anatomy

• Valve motion

• Regurgitant blood flow

• Cardiac-chamber dimensions

• Great-vessel dimensions

• Ventricular function

• Pressure estimates

• Evidence of pulmonary hypertension

• Congenital defects

• Endocarditis lesions

Regurgitant jet size must be interpreted with chamber dimensions and ventricular function rather than used alone. (Tierspital Zürich)

Electrocardiography

A resting ECG identifies persistent rhythm abnormalities.

A 24-hour Holter ECG may be used when an arrhythmia is intermittent. An exercising ECG evaluates how heart rate and rhythm behave at the horse’s normal workload and during recovery.

Exercising ECG is commonly recommended for moderate-to-severe mitral or aortic regurgitation and when collapse, poor performance or ventricular ectopy is a concern. It should not be performed in horses with congestive heart failure, severe valve disease with atrial fibrillation, pulmonary hypertension, markedly reduced function or dangerous ventricular arrhythmias. (Tierspital Zürich)

Blood Pressure and Blood Tests

Additional tests may include:

• Non-invasive blood pressure

• Complete blood count for anaemia or infection

• Biochemistry and electrolytes

• Cardiac troponin I when myocardial damage is suspected

• Blood cultures when endocarditis is possible

A widening pulse pressure and strongly bounding pulse can support haemodynamically significant aortic regurgitation. (Tierspital Zürich)

Can a Horse With a Heart Murmur Still Be Ridden?

Often, yes.

Many horses with physiologic murmurs or mild, stable valve regurgitation can continue their normal work when:

• Performance is normal

• Cardiac chambers remain normal or only minimally enlarged

• Ventricular function is normal

• No dangerous arrhythmia is present

• The lesion is stable on follow-up

• The workload is appropriate

The decision becomes more cautious as the intensity of the sport and consequences of collapse increase.

A quiet trail horse and an eventer galloping cross-country do not carry the same safety exposure, even if their echocardiographic findings are identical.

When Should a Horse Not Be Ridden?

Horses should not be ridden or driven when they have:

• Congestive heart failure

• Pulmonary hypertension

• Complex ventricular arrhythmias

• Severe reduction in cardiac function

• Unexplained collapse

• Severe valve disease with secondary atrial fibrillation

• Severe respiratory distress

Consensus guidance also states that horses with severe aortic regurgitation should not be used by children, as lesson horses or in high-risk sports because of the potential for sudden cardiac death. (Tierspital Zürich)

How Often Should a Heart Murmur Be Rechecked?

The monitoring interval depends on the lesion.

A practical framework is:

Finding	Typical monitoring approach
Physiologic murmur	Recheck during routine examinations
Mild stable mitral regurgitation	Approximately every 12–24 months
Moderate-to-severe mitral regurgitation	At least annually, often with exercise ECG
Mild stable aortic regurgitation	Initial repeat examination, then longer intervals if unchanged
Moderate-to-severe aortic regurgitation	Approximately every six months initially, then annually if progression is minimal
Moderate-to-severe tricuspid regurgitation	Usually annual echocardiography
Any murmur with changing performance or rhythm	Reassess immediately rather than waiting for the scheduled review

Serial echocardiography is more useful for predicting progression than a single examination because it shows whether chamber size, valve function or rhythm is changing over time. (Tierspital Zürich)

Do Heart Murmurs Need Treatment?

The murmur itself is not treated. The underlying cause and its consequences are treated.

No Treatment May Be Needed

Physiologic murmurs and mild stable regurgitation generally require monitoring rather than medication.

Endocarditis

Infective endocarditis requires prolonged, culture-guided antimicrobial therapy and supportive treatment. Prognosis depends on the organism, valve affected, extent of damage and whether heart failure or embolic complications have developed. (PubMed Central (PMC))

Arrhythmias

Atrial fibrillation or ventricular arrhythmias may require specific treatment, exercise restriction or referral. The decision depends on the rhythm, underlying structural disease and the horse’s intended use.

Congestive Heart Failure

Treatment may include diuretics and management of the underlying complication. Evidence for routine use of ACE inhibitors in horses with valve regurgitation but no heart failure remains limited, and no consensus supports giving them simply because a murmur exists. (Tierspital Zürich)

There is currently no routine surgical valve repair equivalent to that used in human cardiac patients for adult horses.

What Is the Prognosis?

Favourable Prognosis

The outlook is generally good when:

• Regurgitation is mild

• The murmur remains unchanged

• Cardiac chambers are normal

• Ventricular function is normal

• Performance is normal

• No arrhythmia is present

• The horse is older when mild aortic regurgitation first appears

Intermediate Prognosis

The prognosis becomes less predictable with:

• Moderate regurgitation

• Mild-to-moderate enlargement

• A progressively louder murmur

• A changing pulse

• Reduced exercise performance

• Development of an arrhythmia

Guarded Prognosis

More serious indicators include:

• Severe chamber enlargement

• Progressive remodelling

• Reduced ventricular function

• Pulmonary hypertension

• Congestive heart failure

• Atrial fibrillation secondary to structural disease

• Ventricular tachycardia

• Ruptured chordae tendineae

• Endocarditis

• Collapse

Most mild lesions are well tolerated. Severe structural disease combined with arrhythmia or heart failure presents a much greater risk to the horse and rider. (Tierspital Zürich)

What Else Can Cause Poor Performance or Collapse?

A murmur may be incidental rather than the true reason a horse is performing poorly.

Other important causes include:

• Upper-airway obstruction

• Equine asthma

• Anaemia

• Lameness

• Back pain

• Gastric ulcers

• Exertional rhabdomyolysis

• Heat stress

• Electrolyte abnormalities

• Primary atrial fibrillation without structural disease

• Neurological disease

• Internal bleeding

• Aortic rupture

• Severe colic

• Toxin exposure

The mistake I see most often is either blaming every performance issue on a mild murmur or dismissing the murmur before establishing whether the heart is enlarging or electrically unstable.

Common Heart-Murmur Mistakes

Assuming Every Murmur Means Heart Failure

Many murmurs are physiologic or associated with mild valve leakage.

Assuming a Soft Murmur Is Harmless

Timing, duration and structural effects matter more than loudness alone.

Assuming a Loud Musical Murmur Must Be Severe

Musical vibration can make aortic regurgitation sound dramatic without proving a large leak.

Ignoring a Diastolic Murmur

A persistent left-sided holodiastolic murmur should be treated as aortic regurgitation until proven otherwise.

Riding Through Collapse or Weakness

A horse that has collapsed or become disoriented during exercise should not return to work until properly investigated.

Assuming Every Irregular Resting Rhythm Is Abnormal

Second-degree atrioventricular block and other vagally mediated rhythms are common in resting fit horses and should disappear with sympathetic stimulation or exercise. Persistent or exercise-associated arrhythmias are different. (Tierspital Zürich)

Skipping Follow-Up Because the First Scan Was Reassuring

Progression is recognised by comparing serial examinations, not by relying indefinitely on one old echocardiogram.

Can Heart Murmurs Be Prevented?

Many age-related or congenital murmurs cannot be prevented.

The practical goal is earlier detection and prevention of complications.

Helpful measures include:

• Annual veterinary examinations

• Careful cardiac assessment before purchase

• Recording the murmur’s grade, timing and location

• Monitoring exercise recovery

• Investigating new fever or weight loss promptly

• Using aseptic techniques around intravenous catheters

• Managing jugular thrombophlebitis aggressively

• Avoiding cardiotoxic feed contamination

• Rechecking known valve disease at the recommended interval

• Stopping exercise when collapse, weakness or abnormal recovery occurs

Frequently Asked Questions

Can a Horse With a Grade 2 Murmur Still Compete?

Often, yes. A grade 2 physiologic murmur or mild valve leak may have no effect on performance. Timing, location, echocardiographic findings and rhythm matter more than the number alone.

Is a Grade 3 Heart Murmur Serious in a Horse?

Not automatically, but a grade 3 left-sided murmur compatible with mitral or aortic regurgitation generally warrants echocardiography, especially in a performance or prepurchase examination. (Tierspital Zürich)

Can a Heart Murmur Disappear?

A functional murmur caused by fever, anaemia, pain or increased cardiac output may lessen after the underlying condition resolves. A murmur caused by degenerative valve disease usually persists.

Does Aortic Regurgitation Always Get Worse?

No. Mild aortic regurgitation in older horses may remain stable for years. Progression is more concerning when the horse is younger, the pulse becomes bounding, the heart enlarges or ventricular arrhythmias develop. (Tierspital Zürich)

Can a Heart Murmur Cause Sudden Death?

Most murmurs do not. The risk becomes more important with moderate-to-severe aortic regurgitation, major structural disease, complex ventricular arrhythmias, pulmonary hypertension or heart failure. (Tierspital Zürich)

Final Thoughts

A heart murmur in a horse is a finding that needs interpretation, not an automatic diagnosis of heart failure.

The key points are:

1. Heart murmurs are common in horses, particularly athletes.

2. Some are caused by completely normal blood flow.

3. Murmur grade describes loudness, not disease severity.

4. Timing, location, duration and character help identify the cause.

5. Mild mitral, tricuspid and aortic regurgitation may be well tolerated.

6. Aortic regurgitation is common in older horses and produces a diastolic murmur.

7. Mitral regurgitation produces a systolic murmur over the left apex.

8. Tricuspid regurgitation is often training-associated but still requires interpretation.

9. Ventricular septal defect is the most common congenital cardiac defect in horses.

10. A new murmur with fever raises concern for endocarditis.

11. Echocardiography determines whether the heart is structurally affected.

12. Resting, Holter and exercising ECGs assess rhythm and safety.

13. Chamber enlargement, arrhythmias and progression matter more than sound alone.

14. Many horses with mild stable murmurs can continue working normally.

15. Collapse, breathing difficulty, heart failure or complex ventricular arrhythmias require immediate action.

The mistake that causes the most harm is reacting only to the sound. The important questions are what is producing the murmur, whether the heart is changing over time and whether the horse remains safe for the work being asked of them.

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ASK A VET™ can help you organise the murmur description, exercise history, heart-rate records, echocardiographic findings and follow-up questions while you work directly with your attending equine veterinarian or cardiologist. A horse with collapse, severe weakness, breathing difficulty, frothy nasal discharge or a dangerous arrhythmia still requires immediate hands-on veterinary care.