By Dr Duncan Houston
A heart murmur at a puppy or kitten check can be worrying, especially when your animal seems completely well. Pulmonic stenosis is one possible explanation, but a murmur alone cannot tell you the diagnosis or whether treatment is needed.
The useful next step is to establish where blood flow is obstructed and how much strain this puts on the heart. Those findings guide monitoring, exercise advice and any specialist procedure.
Quick Answer
Pulmonic stenosis is narrowing of the passage carrying blood from the right side of the heart towards the lungs, usually caused by an abnormally formed pulmonary valve. It is one of the common congenital heart defects in dogs and is uncommon in cats. An ultrasound examination of the heart determines the severity: mild cases often need monitoring, while more significant obstruction may benefit from a specialist procedure. Collapse, difficulty breathing or blue-grey gums require immediate veterinary care.
What causes pulmonic stenosis?
The condition is generally present from birth. The pulmonary valve flaps may be thickened or partly joined together, and the supporting valve ring can also be too small. Narrowing may instead occur below or above the valve, or at more than one level.
The right ventricle, the chamber pumping blood to the lungs, must push against this obstruction. Its muscle can thicken, and severe disease can eventually cause right-sided heart failure. English and French Bulldogs, Boxers and Beagles are among the dog breeds with recognised predispositions, although breed alone does not establish the diagnosis. The MSD Veterinary Manual explains the anatomy and species differences.
What signs might you notice?
Many affected dogs have no obvious signs when the murmur is discovered. More significant disease can cause tiring quickly, fainting, breathing changes or a swollen abdomen from fluid accumulation. Dangerous heart rhythms and sudden death are possible complications, but a single percentage cannot predict an individual dog's risk. See CVCA's explanation of pulmonic stenosis in dogs.
In affected cats, poor growth, reduced activity, weakness or abdominal fluid may occur. Because this defect is unusual in cats, a feline murmur needs investigation without assuming the same cause or treatment plan as a dog's. The MSD overview of congenital heart disease in cats describes these differences.
How do vets confirm the diagnosis?
Echocardiography, an ultrasound scan of the heart, is the key examination. It shows the valve, the location of the narrowing, the right heart's response and any additional defects. Doppler ultrasound measures blood-flow speed, allowing the cardiologist to estimate the pressure difference, or gradient, across the obstruction.
In dogs with primarily valvular stenosis, a gradient above 80 mmHg commonly prompts a recommendation for balloon treatment. Intermediate results require individual assessment. This is a canine treatment guide, not a number for owners to apply to cats or interpret without the rest of the scan. Cornell explains how the gradient helps guide treatment.
Chest X-rays can help assess heart size and the lungs. An electrocardiogram records the heart's electrical rhythm; longer monitoring may be useful when a dog has intermittent collapse or suspected rhythm disturbances. An ultrasound and a rhythm recording answer different questions, as explained in Cornell's guidance on abnormal heart rhythms.
How serious is the finding?
The categories below describe the veterinary assessment. How lively your animal looks at home cannot reliably grade the obstruction. The cardiologist combines the scan, symptoms and associated abnormalities when recommending care.
| Assessment | What it means | Next step |
|---|---|---|
| Mild, with no concerning signs | Limited obstruction; many dogs remain well without medication. | Agree on a recheck schedule and suitable activity. |
| Moderate | The obstruction warrants closer assessment, particularly if symptoms or other defects are present. | Discuss monitoring and possible intervention with a cardiologist. |
| Severe | Substantial obstruction, sometimes despite few outward signs. | Arrange specialist treatment planning promptly; do not wait for fainting. |
| Collapse or breathing distress | A potentially unstable circulation or another serious problem. | Seek emergency veterinary care immediately, regardless of the previous grade. |
What else could cause a murmur or collapse?
Some young animals have innocent murmurs without a structural defect. Others have a different congenital problem, such as a patent ductus arteriosus or a hole between heart chambers. A loud murmur or symptoms need investigation rather than an assumption that the animal will grow out of it. The MSD guide to puppy murmurs and congenital defects explains this distinction.
In cats, hypertrophic cardiomyopathy is a much more common heart disease than pulmonic stenosis. It affects the heart muscle and requires a different assessment and treatment plan. Cornell's feline cardiomyopathy guidance describes the condition.
Collapse can also result from a heart rhythm problem, including one unrelated to the valve narrowing. Tell the vet what happened just before the episode, how long it lasted and how your animal recovered. A video can help if someone can record safely, but obtaining one must never delay care.
When is this an emergency?
Go to an emergency veterinary service now for:
- Collapse or fainting, even if your dog or cat appears to recover.
- Laboured breathing, struggling for air or open-mouth breathing in a cat.
- Blue-grey or very pale gums, or profound weakness.
Breathing difficulty and abnormal gum colour are immediate-care signs in the MSD emergency checklist. Stop activity, minimise handling and call the emergency clinic while arranging transport. Do not make your animal walk to test whether they have recovered or give extra heart medication unless the treating vet directs it.
How is pulmonic stenosis treated?
Balloon valvuloplasty
For suitable dogs with significant narrowing at the valve, a specialist passes a catheter through a blood vessel and positions a balloon across the valve. Inflating it widens the restricted opening and reduces the pressure the heart must generate. General anaesthesia is required. The aim is better blood flow and less cardiac strain; the response varies between animals. CVCA describes balloon valvuloplasty and other cardiac procedures.
The anatomy matters. An unusually small valve ring, narrowing at several levels or an abnormal coronary artery can change the procedure's suitability. Suspected coronary abnormalities may require CT or angiography before treatment is chosen. Selected complex cases may be considered for another intervention or surgery after specialist assessment.
Medication and care in cats
Medication does not physically open the malformed valve. A cardiologist may prescribe a beta blocker in selected dogs, or treatment for an abnormal rhythm or heart failure. These drugs are not automatically required for every murmur. The MSD treatment recommendations cover both intervention and medical management.
A cat's options depend on the precise obstruction and the rest of the heart examination. Medication can help manage complications, and an intervention may be considered in selected cases. Ask the cardiologist which evidence applies to your cat rather than relying on canine success figures.
What happens after a procedure?
Before discharge, obtain written instructions for wound care, activity, medication and rechecks. Ask which complications should trigger an immediate return and when a repeat scan will assess the remaining obstruction. Hospital stay and medication duration depend on the individual patient; there is no single recovery schedule for every dog or cat.
What should you do next?
- If a murmur has just been found: ask whether a cardiology referral is needed and how soon the scan should happen. Do not wait for symptoms to organise a recommended investigation.
- Until activity advice is clear: avoid strenuous exercise or games that provoke exhaustion. Ask what gentle walks or play are appropriate for your animal.
- Keep a simple record: note appetite, energy, breathing at rest, exercise tolerance and changes in abdominal size. Contact your vet the same day about new persistent changes; collapse or breathing distress means emergency care.
- Before anaesthesia: tell the veterinary team about the diagnosis, including before neutering or dental treatment, and share the cardiology report.
- At every review: confirm the next appointment and exactly which changes should bring it forward. Never adjust prescribed medication yourself.
For animals receiving heart-failure medication, follow-up blood tests may also be needed to assess kidney function and electrolytes. CVCA's heart-failure guidance explains monitoring during treatment.
Common mistakes to avoid
- Assuming an energetic puppy cannot have significant heart disease.
- Treating the loudness of a murmur as the complete diagnosis.
- Waiting for another fainting episode before seeking care.
- Expecting medication, supplements or diet to widen a malformed valve.
- Assuming a successful balloon procedure removes the need for follow-up.
Can pulmonic stenosis be prevented?
You did not cause a congenital valve defect through ordinary feeding, walking or play. Early veterinary examinations help identify murmurs, and appropriate cardiac screening is valuable before breeding. Dogs diagnosed with pulmonic stenosis should not be bred because an inherited contribution is recognised or suspected in affected lines. Discuss family history and screening with your vet.
Frequently asked questions
Can a dog live a normal life with pulmonic stenosis?
Many dogs with mild disease have a good outlook. With more severe disease, the outlook depends on the anatomy, complications and response to treatment. An individual scan is more useful than a general life-expectancy figure.
Will my puppy grow out of pulmonic stenosis?
A confirmed structural narrowing should not be expected to disappear as an innocent puppy murmur might. Follow the investigation and recheck plan your vet recommends.
Does every dog with pulmonic stenosis need balloon treatment?
No. Mild cases often need monitoring. Moderate or severe cases warrant a specialist discussion, and the exact anatomy determines whether balloon treatment is suitable.
Can cats have pulmonic stenosis?
Yes, but it is uncommon. An ultrasound is needed to confirm the obstruction and assess other possible heart disease. Treatment decisions must be made for that cat.
Is balloon valvuloplasty a permanent cure?
It can substantially relieve suitable valve narrowing, but improvement is variable and some obstruction may remain. Follow-up examinations establish the benefit and guide ongoing care.
The next decision is based on the scan
A murmur is the starting point for investigation. Ask for a clear explanation of the severity, the anatomy and the recommended next step. Keep planned reviews even when your dog or cat seems well, and treat collapse or breathing difficulty as an emergency.
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