Pulmonary Hypertension in Dogs: Fainting, Breathing Signs and Treatment

By Dr Duncan Houston

A dog that faints on a short walk or struggles to breathe may have a heart or lung problem, including pulmonary hypertension. This means pressure is abnormally high in the circulation supplying the lungs.

It is different from the systemic blood pressure measured with a cuff. The cause matters because treatments suitable for one form can be unsuitable for another.

Quick Answer

Pulmonary hypertension can cause reduced exercise tolerance, fainting, coughing and breathing difficulty. Vets usually assess its probability with an echocardiogram alongside tests for underlying heart, lung, clotting or parasitic disease. Treatment is tailored to the cause and may include specific pulmonary blood-vessel medication. Collapse or laboured breathing requires emergency assessment.

Why does pressure rise in the lungs?

Blood normally passes from the right side of the heart through the lungs at relatively low pressure. Lung disease, low oxygen, clots, parasites and some congenital abnormalities can increase resistance. Left-sided heart disease can also transmit pressure backward into the lung circulation.

The ACVIM consensus guidance on canine pulmonary hypertension groups causes to guide diagnosis and treatment. A label of pulmonary hypertension is therefore the beginning of a management plan, not a complete explanation.

Which signs are important?

Dogs may tire quickly, stop during walks, breathe faster at rest or faint during activity or excitement. A cough is possible but is not specific. Advanced disease can strain the right heart and contribute to abdominal fluid accumulation.

Record an event only if it is safe and does not delay help. A description of what happened before and after collapse can help distinguish fainting from other events.

How is it diagnosed?

Echocardiography examines heart structure, blood flow and changes consistent with increased pulmonary pressure. Doppler measurements estimate pressure differences; they are interpreted with other findings rather than used as a single infallible number.

Chest imaging, bloodwork, oxygen assessment and targeted tests for heartworm, lungworm or clotting-associated disease may be appropriate. The local parasite risks and travel history matter. Direct pressure measurement by catheter is not routinely performed in most pet dogs.

What else could cause these signs?

Abnormal heart rhythms, congestive heart failure, airway collapse, anaemia, lung disease and seizures are among the alternatives. Several can coexist with pulmonary hypertension. For example, a cough in an older small dog may involve both airway disease and a heart murmur without proving heart failure.

How is it treated?

Treatment targets the cause and the effects on breathing and circulation. Oxygen and hospital stabilisation may be needed in a crisis. Some dogs benefit from sildenafil or another prescribed pulmonary vasodilator, but this is not automatically appropriate for every form of disease.

In dogs with left-heart disease, the risk of pulmonary oedema influences decisions about vasodilators. Diuretics are used when relevant fluid congestion is present, not simply because a dog coughs. Antithrombotic or parasite treatment is selected when indicated by the underlying diagnosis.

The published ACVIM consensus statement emphasises individual classification and monitoring. There is no single survival estimate that usefully covers all causes and severities.

When is this an emergency?

Go immediately for laboured breathing, blue-grey gums, persistent collapse or marked weakness. Keep your dog cool and quiet, minimise exertion and call ahead. Do not force tablets, food or water into a dog struggling to breathe.

A practical home-care plan

1. Ask what activity is safe. Keep exercise gentle and stop before distress develops.
2. Avoid heat, intense excitement and situations that have triggered collapse.
3. Give prescribed medicines consistently and clarify what to do after a missed dose.
4. Count sleeping breaths as your vet advises and record changes from your dog’s baseline.
5. Track fainting, appetite, walking tolerance and abdominal enlargement.
6. Attend planned imaging and laboratory checks; report deterioration sooner.

Common mistakes

• Assuming a normal cuff blood pressure excludes pulmonary hypertension.
• Continuing a walk after a fainting episode because the dog recovered.
• Starting sildenafil or increasing diuretics without veterinary advice.
• Using one internet survival figure to make decisions for every dog.

Prevention and ongoing support

Not every cause is preventable. Appropriate parasite prevention, weight management, smoke avoidance and management of existing heart or lung disease can reduce avoidable burdens. Choose quiet enrichment and scent activities when strenuous exercise is restricted.

Frequently asked questions

Is this the same as ordinary high blood pressure?

No. It concerns blood pressure in the pulmonary circulation rather than the systemic arteries.

Can dogs improve with treatment?

Some improve meaningfully, depending on cause, severity and response. Monitoring remains important.

Should all affected dogs rest completely?

Activity should be individualised. A stable dog may tolerate gentle activity, while unstable dogs need strict veterinary guidance.

The safest plan connects the pressure finding with its cause and gives you clear limits for activity, monitoring and emergency care.

For help understanding your animal’s care and preparing questions for your veterinarian, visit ASK A VET™. Seek in-person emergency care immediately for urgent signs.