Why Does Your Dog Keep Fainting and Getting Winded on Walks?

If your dog has been coughing, tiring out faster than usual, or had a fainting episode, and your vet mentioned pulmonary hypertension, here’s what that actually means: it’s abnormally high blood pressure in the arteries running between the heart and the lungs. That extra pressure forces the heart to work much harder than it should, reducing how much oxygen gets into the bloodstream. It’s usually a consequence of another underlying disease, not a standalone diagnosis.

What are the signs of pulmonary hypertension in dogs?

PH in dogs tends to creep up gradually, so the early signs are easy to miss or chalk up to aging. Here’s what to look for:

• Exercise intolerance: Your dog gets winded quickly, stops wanting to walk as far, or seems exhausted after minimal activity.
• Coughing: A persistent, dry, or honking cough that doesn’t go away with rest.
• Labored breathing: Fast, shallow, or effortful breathing even when your dog isn’t moving around.
• Fainting or collapsing (syncope): Brief episodes where your dog goes limp or loses consciousness, often triggered by excitement or exertion.
• Blue or purple-tinged gums (cyanosis): A sign that not enough oxygen is getting into the blood. This is an emergency.
• Distended belly: Fluid buildup in the abdomen, which can happen as the heart struggles under the pressure.

If you’re seeing blue gums or a fainting episode, don’t wait for a scheduled appointment. Head to an emergency vet.

What causes pulmonary hypertension in dogs?

PH is almost never the primary problem. It’s usually the result of something else putting stress on the heart-lung system. The most common culprits:

• Heartworm disease: Parasitic worms that live in the heart and pulmonary arteries, physically blocking blood flow and triggering inflammation.
• Chronic lung disease: Conditions like pulmonary fibrosis (scarring of the lung tissue) or chronic bronchitis that reduce oxygen levels over time.
• Left-sided heart disease: Mitral valve disease, one of the most common heart conditions in dogs, can cause back pressure that eventually affects the pulmonary arteries.
• Pulmonary thromboembolism: Blood clots that travel to the lungs and block blood flow, causing a sudden spike in pulmonary pressure.
• Other causes: Liver disease, Cushing’s disease (a hormonal condition), and certain cancers can also contribute.

How do vets diagnose PH in dogs?

The go-to diagnostic tool is an echocardiogram, essentially an ultrasound of the heart. It lets the cardiologist measure blood flow and estimate the pressure in the pulmonary arteries without invasive procedures. It’s painless for your dog and usually takes 30 to 60 minutes.

Your vet will likely also run chest X-rays (to check lung and heart size), bloodwork, and possibly a heartworm test or other imaging, depending on what underlying cause they suspect. The goal is to confirm PH and figure out what’s driving it, because treatment depends heavily on the root cause.

How is pulmonary hypertension in dogs treated?

There’s no single fix for PH, but there are real tools that can help manage it. Your vet may recommend:

• Sildenafil (the same drug as Viagra, used at veterinary doses): It relaxes and widens the pulmonary arteries, reducing the pressure the heart has to push against. Most dogs tolerate it well, and it’s often taken once or twice daily, long-term.
• Treating the underlying cause: Heartworm treatment, managing chronic lung disease, or addressing mitral valve disease with appropriate medication can all reduce the pressure load on the heart.
• Diuretics: If your dog has fluid buildup in the belly or lungs, a diuretic (AKA a medication that helps the body shed excess fluid) may be added.
• Oxygen therapy: In more severe cases, supplemental oxygen may be used at home or during vet visits.

Always follow your vet’s recommendations rather than adjusting medications on your own. Dosing for sildenafil in dogs is specific to their weight and condition.

At-home management guide for dogs with PH

Most of what keeps a dog with PH comfortable and stable happens between vet visits. Here’s what a practical daily routine looks like.

Keep activity gentle and predictable

Short, calm walks are usually fine, but skip anything that gets your dog panting heavily. Avoid fetch, running, rough play, and activities in heat or humidity, all of which make the heart and lungs work harder than they need to. Try to avoid sudden bursts of excitement too, since those can trigger fainting episodes in some dogs.

Manage heat and stress

Heat increases the body’s demand for oxygen, which is the last thing a dog with PH needs. Keep your dog cool in warm months, limit outdoor time in high temperatures, and aim for a calm, low-stress home environment. Anxiety and overexcitement put extra strain on an already-stressed heart.

Track their resting respiratory rate

This is one of the most useful habits you can build. While your dog is fully relaxed and asleep, count how many times their chest rises in 60 seconds. A normal resting respiratory rate for dogs is under 30 breaths per minute. Log it daily at the same time each day. If it climbs above 30, or jumps noticeably from their usual baseline, call your vet. This single number can catch a decline before visible symptoms worsen.

Know when to go to the emergency vet

Some signs can’t wait. Go straight to an emergency vet if your dog:

• Faints or collapses, even briefly
• Has blue, gray, or white gums
• Is breathing rapidly and can’t seem to catch their breath at rest
• Seems confused or can’t stand after an episode

These are signs of a cardiac or respiratory crisis. Don’t wait to see if things improve on their own.

Prognosis and what to expect

Pulmonary hypertension dog prognosis varies a lot depending on what’s causing it and how advanced it is at diagnosis. If the underlying condition is treatable (like heartworm or a reversible lung issue), managing it well can significantly improve quality of life and slow progression. If PH is caught early and responds to sildenafil, some dogs do well for a year or more.

End stage pulmonary hypertension in dogs is harder. When the right side of the heart begins to fail under the sustained pressure, symptoms become more difficult to control, and quality of life declines more quickly. That’s why early detection and consistent management matter so much. Your vet or a veterinary cardiologist can give you a clearer picture based on your dog’s specific situation and how they respond to treatment.

Does pet insurance cover pulmonary hypertension in dogs?

Yes, pulmonary hypertension is eligible for coverage under a Lemonade Pet accident and illness policy, as long as the condition isn’t pre-existing. That means your dog shouldn’t be showing any signs or symptoms before your policy starts or during your waiting period.

An echocardiogram, specialist visits, and lifelong medication like sildenafil add up quickly, especially when PH is tied to a condition like heartworm disease or mitral valve disease that requires its own treatment track. Getting coverage in place while your dog is healthy is what makes it actually useful when you need it.

Before we go

Pulmonary hypertension is serious, but dogs who are diagnosed early and managed well can do better than most owners expect. Stay consistent with medication, track that resting respiratory rate, keep activity calm, and lean on your vet and cardiologist as partners in your dog’s care. And if your dog isn’t already covered, now is a good time to look into it.

A few quick words, because we <3 our lawyers: This post is general in nature, and any statement in it doesn’t alter the terms, conditions, exclusions, or limitations of the policies issued, which differ according to your state of residence. You’re encouraged to discuss your specific circumstances with your own professional advisors. The purpose of this post is merely to provide you with info and insights you can use to make such discussions more productive! Naturally, all comments by, or references to, third parties represent their own views, and Lemonade assumes no responsibility for them. Coverage may not be available in all states. Please note that statements about coverages, policy management, claims processes, Giveback, and customer support apply to policies underwritten by Lemonade Insurance Company or Metromile Insurance Company, a Lemonade company, sold by Lemonade Insurance Agency, LLC.  The statements do not apply to policies underwritten by other carriers.