Pulmonary Hypertension in Dogs: Fainting, Breathing Signs and Treatment

By Dr Duncan Houston

A dog that faints during excitement or struggles with gentle activity needs investigation, even if they seem normal again a minute later. Pulmonary hypertension is one possible cause.

The diagnosis describes abnormal pressure in the lung circulation. It does not identify one single disease or one treatment suitable for every dog.

Quick Answer

Pulmonary hypertension means increased pressure in the blood vessels of the lungs, which can strain the right side of the heart. It may occur with heart disease, respiratory disease, parasites, clots or other conditions. Fainting and worsening exercise tolerance need prompt assessment; difficult breathing, blue gums or collapse require emergency care.

Why does the pressure rise?

Blood may encounter increased resistance within lung vessels, or pressure may be transmitted backwards from left-sided heart disease. Low oxygen, lung disease, pulmonary clots and certain parasites can also contribute. More than one cause may be present in the same dog.

The ACVIM pulmonary hypertension consensus groups cases by these underlying mechanisms because treatment depends on the cause. Pulmonary hypertension is not the same measurement as ordinary systemic blood pressure taken with a limb or tail cuff.

What signs can owners see?

Reduced stamina, weakness, rapid or effortful breathing and fainting may occur. Some dogs cough because of associated airway or heart disease. Fluid can accumulate in the abdomen when right-sided heart failure develops. None of these signs alone proves pulmonary hypertension.

What else could cause fainting or breathlessness?

Heart rhythm disturbances, airway obstruction, heart failure, anaemia, low blood glucose and seizures may produce overlapping episodes. A video can help distinguish fainting from a seizure, but recording should never delay assistance. A rapid recovery does not rule out a dangerous problem.

How do vets diagnose it?

Echocardiography assesses heart structure and Doppler blood-flow measurements to estimate the probability and severity of pulmonary hypertension. It does not directly measure pulmonary arterial pressure in the way cardiac catheterisation does. Findings must be interpreted alongside signs and other tests.

Chest imaging, blood tests, parasite testing and sometimes advanced respiratory investigations help identify the underlying disease. An ECG or longer heart-rhythm recording may be needed if episodes suggest an arrhythmia.

When is this an emergency?

Breathing difficulty or a collapse that does not resolve promptly needs immediate treatment. Stop activity, keep the dog cool and calm, minimise handling and phone ahead. Do not force food or water. Avoid neck pressure and do not muzzle a dog that is struggling to breathe.

How is pulmonary hypertension treated?

Treatment may address heart failure, lung disease, parasites or clot risk. Selected dogs benefit from medicines that reduce resistance in the pulmonary circulation, such as sildenafil. These are not suitable automatically for every cause, and inappropriate use can worsen problems in some patients.

Oxygen and hospital support may be needed during a crisis. Prognosis varies substantially with the underlying disease and response, so a single published survival figure should not be used as a countdown for an individual dog.

What should you do at home?

1. Follow medication instructions and ask before changing doses or adding supplements.
2. Use the prescribed activity limits; avoid exertion, overheating and intense excitement.
3. Record sleeping breathing, fainting episodes, appetite and abdominal size as advised.
4. Agree on specific changes that should trigger a call or emergency visit.
5. Attend rechecks so the plan can be adjusted to symptoms and investigations.

Common mistakes and prevention

• Assuming a normal cuff blood pressure excludes pulmonary hypertension.
• Trying to exercise a fainting dog to improve fitness.
• Borrowing heart medication from another animal.
• Ignoring a brief collapse because recovery was quick.

Region-appropriate parasite prevention and management of known heart and respiratory disease reduce avoidable risk, although not every cause is preventable.

Frequently asked questions

Is pulmonary hypertension always heart failure?

No. It can occur without heart failure and may arise from respiratory or vascular disease.

Will sildenafil cure it?

It may improve signs in selected dogs but does not necessarily remove the underlying cause.

Can a dog still have gentle walks?

Sometimes, but activity must match symptoms and the treating vet's advice, especially after fainting.

The useful plan links the pressure problem to its cause, then monitors how your dog feels and breathes in daily life.

Explore ASK A VET™ for clear information about ongoing care. Breathing difficulty or prolonged collapse needs emergency treatment.