Dog Congestive Heart Failure: How to Spot Signs the Safe Way

Congestive heart failure in dogs happens when the heart can no longer pump well enough to keep up with the body’s needs, so fluid backs up, most often into the lungs. The clearest early sign at home is faster or harder breathing while your dog is resting or asleep, often alongside coughing, tiring easily or restless nights. A dog breathing with obvious effort, with blue, grey or very pale gums, or who collapses, needs an emergency vet straight away.

This guide is written for owners, not vets. It explains what a heart murmur is and how it relates to heart failure, the stages vets use, the signs to watch for, how to count your dog’s sleeping breathing rate at home (one of the most useful monitoring tools available to owners), and when a change means “ring today” or “go now”. It does not cover medicines; those decisions belong to your vet, who knows your dog.

At a glance

• A heart murmur is a sound the vet hears through a stethoscope. Many dogs with a murmur never develop heart failure, but a murmur in an adult dog deserves investigation.
• The most common heart disease in dogs is a slow, age-related problem with the mitral valve, seen especially in small and medium breeds.
• Faster breathing at rest or during sleep is often the earliest sign that fluid is building up.
• Counting your dog’s sleeping breathing rate takes one minute and gives your vet real numbers to work with.
• Laboured breathing, coloured gums, fainting or collapse are emergencies: go to a vet immediately.

Heart murmurs, heart disease and heart failure: how they connect

These three terms are often mixed up, and the difference matters for how worried you should be.

A heart murmur is an extra “whooshing” sound caused by turbulent blood flow. Vets grade murmurs by loudness, usually on a scale of one to six. Some young puppies have soft, harmless murmurs that fade as they grow. In an adult dog, a new murmur is usually a sign that something has changed in the heart, often a leaky valve, and your vet will want to find out more.

Heart disease means there is a structural or functional problem with the heart. A dog can have heart disease for years without any outward signs at all.

Congestive heart failure (CHF) is the stage where the disease has progressed enough that the heart cannot keep blood moving forward properly. Pressure builds up behind the struggling side of the heart and fluid leaks out of blood vessels. When the left side is affected, fluid collects in the lungs, which is why breathing changes are such an important sign. When the right side is affected, fluid can collect in the belly, causing a swollen abdomen.

The two diseases owners hear about most

The most common acquired heart disease in dogs is myxomatous mitral valve disease (MMVD), sometimes called degenerative valve disease. The valve between the two left chambers slowly thickens and leaks. It is especially common in smaller breeds, and veterinary research highlights breeds such as the Cavalier King Charles Spaniel, Poodle, Pomeranian, Chihuahua, Dachshund and Bichon Frise. It usually develops gradually with age.

Dilated cardiomyopathy (DCM) is a disease of the heart muscle itself, which becomes thin and weak. It is seen more often in large and giant breeds. Unlike valve disease, it does not always cause a loud murmur early on, which is one reason regular check-ups matter for at-risk breeds. If you are still choosing a dog, our guide to choosing the right breed explains which health questions to ask breeders.

The stages vets use

For mitral valve disease, most vets use a staging system set out in the American College of Veterinary Internal Medicine (ACVIM) consensus statement, last revised in 2019. Knowing your dog’s stage helps you understand what the vet is monitoring and why.

ACVIM stage	What it means	What owners usually notice	What owners can do
A	A breed at higher risk, with no heart disease found yet	Nothing	Keep up regular health checks so the vet can listen for a murmur
B1	Valve disease is present but the heart has not enlarged	Usually nothing	Follow the vet’s recheck schedule; learn your dog’s normal sleeping breathing rate
B2	Valve disease with enough heart enlargement that the vet may recommend a management plan	Often nothing yet	Count sleeping breathing rate regularly; keep notes; follow the vet’s plan
C	Signs of heart failure now, or in the past	Faster breathing, coughing, tiring easily, restless nights	Daily breathing counts, a clear emergency plan, regular rechecks
D	Advanced heart failure that is hard to control	Signs that return despite management	Close contact with your vet about comfort and quality of life

The key point for owners is that stages B1 and B2 have no outward signs. A dog can look perfectly healthy while the vet is tracking real change, which is why home monitoring is so valuable.

Signs of heart failure in dogs

Signs often creep in slowly, and many owners put them down to age. Watch for:

• Faster breathing while resting or asleep, or breathing that looks like more effort than usual
• Coughing, particularly at night, after lying down or after mild activity
• Tiring sooner on walks, lagging behind or wanting to stop
• Restlessness at night: pacing, getting up repeatedly, or choosing to sit or stand rather than lie down
• Reduced appetite or weight loss, sometimes with loss of muscle along the back
• A swollen belly, which can be a sign of fluid build-up
• Fainting or collapse, especially during excitement or exercise
• Gum colour changes: pale, grey or blue-tinged gums

Many of these signs overlap with other conditions common in older dogs, including lung problems, arthritis and cognitive change. Night-time restlessness, for example, can also be a sign of canine dementia. Only your vet can tell them apart, so report the change rather than guessing the cause.

How to count your dog’s sleeping breathing rate

Counting breaths while your dog sleeps is one of the most useful things an owner can do. Studies published in the Journal of the American Veterinary Medical Association (2013) and The Veterinary Journal (2016), the latter led by Porciello and colleagues, found that dogs with heart disease that had not reached failure, and dogs whose heart failure was well controlled, mostly had average sleeping breathing rates below 30 breaths per minute. A rate that climbs above a dog’s usual level can be an early warning that fluid is returning, sometimes before other signs show.

1. Choose the right moment. Count when your dog is deeply asleep and settled, in a comfortable, cool room. Avoid times straight after exercise, during dreaming twitches, or when they are hot or excited.
2. Watch the chest or belly. One rise and one fall together count as one breath.
3. Count for a full 60 seconds if you can, or count for 30 seconds and double it.
4. Write it down with the date and time. A notebook or a phone note works well.
5. Repeat regularly. In the early stages your vet may suggest a few times a week; in dogs with diagnosed heart failure, many vets suggest daily counts.
6. Learn your dog’s normal. After a couple of weeks you will know their usual range, which makes a change easier to spot.
7. Act on the number. Many vets use a sleeping rate that is consistently above 30 breaths per minute as the point to get in touch. Your vet may give you a personal threshold for your dog; follow theirs.

A single high count may be a fluke, such as a dream or a warm room. Count again when your dog is calmer. A rate that stays high, or creeps up over several days, is the pattern to report.

When to ring the vet and when to go now

What you see	What it may mean	What to do
Sleeping breathing rate within your dog’s usual range; normal energy	Stable	Keep counting; attend scheduled rechecks
Sleeping rate consistently above 30 breaths per minute, or higher than usual over a few days	Possible early fluid build-up	Ring your vet the same day
New or worsening cough, tiring faster, eating less, unsettled nights	Disease may be progressing	Ring your vet the same day for advice
Breathing with obvious effort, open-mouth breathing at rest, refusing to lie down	Fluid in the lungs is likely	Go to an emergency vet now
Blue, grey or very pale gums; fainting; collapse	Not enough oxygen reaching the body	Go to an emergency vet now

If you are unsure, ring. Breathing problems can worsen quickly, and vets would much rather hear from you early. Keep your vet’s out-of-hours number and the nearest emergency clinic saved in your phone. Our calm guide to knowing when to call the vet sets out a simple three-tier plan you can use for any illness.

What happens at the vet

Diagnosis usually begins with listening to the heart and lungs and checking pulse, gum colour and breathing. To confirm heart disease and its stage, your vet may suggest chest X-rays to look at heart size and fluid in the lungs, an echocardiogram (an ultrasound scan of the heart), an ECG to check the heart’s rhythm, and blood tests, including one that measures a marker released when the heart is under strain.

If heart disease is confirmed, your vet will explain the stage and build a plan around it. That plan may include medicines, rechecks and home monitoring. Always follow your vet’s instructions exactly, never adjust or stop prescribed treatment on your own, and never give your dog medicines meant for people.

Living well with a dog who has heart disease

Many dogs with heart disease continue to enjoy a good quality of life with the right monitoring and care. Practical, vet-approved habits include:

• Keeping exercise gentle and steady rather than intense; let your dog set the pace and stop if they tire. Our guide to how much exercise a dog needs explains how to adjust for age and health.
• Avoiding hot weather walks and overheating, which make breathing harder.
• Keeping your dog at a healthy weight, with any diet changes discussed with your vet first.
• Using a harness rather than a collar if pressure on the neck triggers coughing.
• Making rest easy: a comfortable bed in a cool spot, and fewer stairs if they struggle.
• Keeping a single record of breathing counts, coughs, appetite and energy to bring to every appointment.

Heart disease often appears in older dogs, so it sits alongside other age-related changes. Our guide to caring for a senior dog covers the bigger picture, and if you are weighing up the cost of long-term monitoring, our pet insurance guide explains what to check about pre-existing conditions before you buy a policy.

Common mistakes

• Putting slowing down and coughing down to “just old age”. These can be heart signs and deserve a check.
• Counting breaths at the wrong time. Counts taken after play, in the heat or during dreams will read high.
• Not knowing your dog’s normal. Start counting when your vet first finds a murmur, not when you are already worried.
• Waiting until morning with laboured breathing. Breathing with effort at rest is an emergency.
• Changing or stopping medicines without the vet. Always ask first.
• Assuming a murmur means heart failure is coming soon. Many dogs with a murmur stay in the early stages for a long time. Follow-up tells you where your dog actually is.

Sources this guide draws on: the American College of Veterinary Internal Medicine (ACVIM) 2019 consensus guidelines on myxomatous mitral valve disease in dogs, Porciello and colleagues’ 2016 study of sleeping and resting respiratory rates in The Veterinary Journal, and the 2013 Journal of the American Veterinary Medical Association study of sleeping and resting respiratory rates in dogs with subclinical heart disease.

Frequently asked questions

What are the first signs of congestive heart failure in dogs?

The earliest sign is often a faster breathing rate while resting or asleep. Coughing, tiring more easily on walks and restlessness at night are also common early changes. Ring your vet if you notice any of them, especially in a dog already known to have a murmur.

Does a heart murmur mean my dog has heart failure?

No. A murmur is a sound, not a diagnosis, and many dogs with a murmur never develop heart failure. In an adult dog, though, it usually means some heart change is present, so your vet may suggest tests to stage it and a plan for monitoring.

What is a normal sleeping breathing rate for a dog?

Research suggests most dogs, including many with early heart disease, breathe below 30 times a minute while sleeping, and often well below. Your own dog’s normal range is the most useful benchmark, so count regularly and report a rate that stays higher than usual.

Is coughing at night a sign of heart problems?

It can be, especially in an older small-breed dog with a known murmur. Night coughing can also come from airway or lung problems, so it needs a vet check rather than guesswork. Note when the cough happens and how often to help your vet.

Which breeds are most at risk of heart failure?

Mitral valve disease is most common in small breeds, including the Cavalier King Charles Spaniel, and is seen often in Poodles, Pomeranians, Chihuahuas and Dachshunds. Dilated cardiomyopathy is more common in large and giant breeds. Any dog can develop heart disease, so regular checks matter for every dog.

When is heart failure an emergency?

Go to an emergency vet immediately if your dog is breathing with obvious effort, breathing with their mouth open at rest, will not lie down, has blue, grey or very pale gums, faints or collapses. Do not wait to see whether it settles.

Hearing the word “murmur” at a check-up can be frightening, but it is also an opportunity. Learning your dog’s sleeping breathing rate, knowing the warning signs and having an emergency plan ready puts you in the best position to catch changes early and keep your dog comfortable for as long as possible.