Heart failure in dogs: the stages, the signs, and how to monitor at home

If you are reading this, a vet has probably told you that your dog has a heart murmur, or that their heart is enlarged, or used the words "heart failure" and you're wondering what that means for your dog. You may have noticed a soft cough that will not settle, or breathing that looks faster than it should, or a moment where your dog wobbled and went down. Whatever brought you here, the aim of this article is to give you a calm, accurate picture of what is happening and what you can do about it.

Congestive heart failure (CHF) in dogs is the point at which a diseased heart can no longer pump well enough to keep up with the body's needs, so fluid begins to back up behind it. That fluid usually collects in the lungs, causing coughing and fast or laboured breathing, or in the abdomen, causing a swollen belly. The heart disease that leads to it often develops quietly over months or years before the failure stage arrives, which is why so many dogs are diagnosed with a murmur long before they ever seem unwell.

What is congestive heart failure in dogs?

It helps to separate two ideas that often get tangled. The first is the underlying heart disease itself, a leaky valve or a weakened heart muscle, which may be present for a long time while the dog looks and behaves normally. The second is heart failure, the moment that disease tips over into causing real-world symptoms. Many dogs live for a good while in the first phase. Treatment is partly about delaying the move into the second.

What causes it?

In UK dogs, the great majority of congestive heart failure comes from one of two underlying diseases. Which one tends to depend a lot on the size and breed of the dog.

Myxomatous mitral valve disease (MMVD) is by far the most common, especially in small and medium breeds. The mitral valve, which separates the two chambers on the left side of the heart, gradually thickens and stops sealing properly, so blood leaks backwards each time the heart beats. That leak is what a vet hears as a heart murmur, often for years before any failure. Cavalier King Charles Spaniels are particularly prone to it and tend to develop it younger than other breeds, but it is common across small breeds generally. Often, the first sign is a murmur picked up during a routine examination. Months or even years later, coughing may develop as the heart enlarges and fluid begins to accumulate in the lungs.

Dilated cardiomyopathy (DCM) is the large and giant breed disease. Here the heart muscle itself becomes weak and the chambers stretch and enlarge, so the heart pumps poorly. Dobermanns and Great Danes are over-represented, along with other big breeds. DCM can be more treacherous than MMVD because it sometimes causes dangerous heart rhythm disturbances, which means some dogs collapse suddenly, or are lost suddenly, before obvious congestive signs ever appear. This is why screening at-risk breeds matters.

There are other, less common causes, including some congenital defects and disease of the heart's lining or rhythm, but for most families it is one of these two.

What are the signs and stages?

UK vets describe heart disease using a staging framework from the American College of Veterinary Internal Medicine (ACVIM), which is used internationally. It runs from at-risk through to end-stage, and knowing roughly where your dog sits helps you understand what to watch for and what treatment is for.

• Stage A. The dog is a breed at risk (for example a Cavalier, a Dobermann) but has no detectable heart disease yet. Nothing to treat, but worth periodic listening.

• Stage B. Heart disease is present, often heard as a murmur, but the dog has no symptoms. This stage is split in two. B1 means the heart is not yet significantly enlarged. B2 means the leak or weakness has caused meaningful enlargement of the heart. The distinction matters, because in B2 MMVD there is good evidence that starting the drug pimobendan delays the onset of heart failure.

• Stage C. The dog has developed clinical congestive heart failure, the signs below, and needs active treatment. Most dogs respond well to that treatment, at least for a time.

• Stage D. End-stage or refractory failure, where standard doses of medication are no longer holding the signs and breathlessness becomes hard to control.

The signs tend to arrive gradually. Early on there may be nothing at all beyond a murmur. As things progress you may notice reduced stamina on walks, then a cough, particularly at night or after lying down, then faster or harder breathing, including a rise in the resting and sleeping breathing rate covered below. Some dogs have episodes of fainting or collapse (syncope), which can be frightening to see but is often brief. In disease affecting the right side of the heart, fluid builds in the abdomen instead, so you may see a swollen, rounded belly (ascites) and weight or muscle loss over the back end.

None of these signs alone confirms heart failure, and a cough in particular has many other causes in older dogs. It is the pattern, and a known heart murmur sitting behind it, that points the way.

How is it diagnosed?

Your vet will usually suspect heart disease from the examination, but imaging is what confirms exactly what is happening.

The aim is to confirm whether fluid has actually backed up, and to work out which underlying disease is driving it and which stage it has reached.

The single most useful test is an echocardiogram, an ultrasound scan of the heart, which shows the valves, the muscle, and how enlarged the chambers are. This is what separates B1 from B2 and confirms MMVD versus DCM. Chest X-rays show whether fluid has collected in the lungs and how big the heart has become. Vets may also use an ECG if the rhythm sounds irregular, blood pressure measurement, and sometimes a blood marker called NT-proBNP that rises when the heart is under strain. Kidney bloods are usually checked too, because heart and kidney function are closely linked and the medications interact with both.

What does treatment involve?

The cornerstone medications are a small, well-established group. Pimobendan helps the heart pump more strongly and relaxes the blood vessels, and in MMVD it is also used earlier, in Stage B2, to delay failure starting at all. Diuretics, usually furosemide or torasemide, draw the excess fluid off the lungs or abdomen and are what relieve the breathlessness most directly. An ACE inhibitor and spironolactone are often added to ease the load on the heart and counter the hormonal changes that drive the disease forward. The exact combination and doses are tailored to the dog and adjusted over time, which is why repeat checks and bloods matter.

It is fair to be honest about what this does and does not achieve. The medication does not cure the underlying valve or muscle disease, and it does not stop it progressing. What it does, often very effectively, is buy comfortable, good-quality time, and for many dogs that time is measured in a useful stretch of months and sometimes longer. Doses usually need increasing as the disease advances.

How can I monitor my dog at home?

The most useful thing you can do at home is learn to count your dog's sleeping respiratory rate, the number of breaths they take per minute while genuinely asleep. It is a simple, established cardiology tool, and a sustained rise is one of the earliest signs that fluid is starting to build, often before a cough or any obvious breathlessness appears.

To do it, wait until your dog is settled and asleep, not panting from heat or a recent walk. Watch the chest and count one breath as a full in-and-out, for a full minute (or count for fifteen seconds and multiply by four). As general cardiology guidance, most healthy dogs breathe comfortably below about 30 breaths per minute when resting or asleep. The important number is your own dog's normal baseline when they are well: take it on several calm evenings and note it down. A resting or sleeping rate that climbs and stays consistently above their usual baseline, or persistently over roughly 30 breaths a minute, is a reason to ring your vet, even if your dog seems otherwise alright. Keeping a short note of the figure a few times a week gives you and your vet an early, objective warning.

Alongside that, watch the things that change slowly: stamina on walks, appetite, any cough, the shape of the belly, and how your dog is in themselves. If you have a dog with diagnosed heart disease, your vet will tell you which signs should prompt an urgent call.

When does it become a quality-of-life question?

Congestive heart failure is a progressive disease, and there is a point, Stage D, where standard medication can no longer reliably control the breathlessness. The honest reality is that breathing distress is one of the hardest symptoms to live with, for a dog and for the people watching, and it is the point at which the conversation gently turns from treatment to comfort.

What that looks like in practice is breathlessness or coughing that no longer settles with the current tablets, a dog who is tiring with very little effort, repeated fluid build-up that needs ever-higher doses, broken nights, and a clear loss of the things they used to enjoy. The most distressing version is acute fulminant pulmonary oedema, a sudden flooding of the lungs that leaves a dog gasping and frightened, and that usually means an urgent dash to an out-of-hours clinic. One of the kindest things planning ahead can do is take that night-time emergency off the table, so that if the time comes it can be calm, at home, and on your terms rather than in a panic.

Our Quality of Life assessment is a short, structured tool to help you think it through. It is not there to give you a number that decides for you. It is there to give shape to what you are already noticing across appetite, comfort, breathing, mobility, and the small pleasures your dog still has.

Because heart and kidney function are so closely linked, dogs on long-term heart medication sometimes develop kidney strain as well, and the two have to be balanced against each other. If that is part of your dog's picture, our guide to kidney disease in dogs covers that side in more detail, and our piece on when is it time walks through the decision itself.

How we can help

We are a vet-led at-home service. When the time comes, our visiting vets come to you, take time to explain everything, and use sedation first so your dog is calm and settled before the final injection. For a dog whose breathing is the problem, being able to stay in their own familiar room, with no stressful car journey, often matters a great deal. Our home euthanasia for dogs is built for exactly that.

If you would simply like to talk through where your dog is, with no obligation either way, the line is open seven days a week, including evenings and weekends. There is no script and no pressure, only time to listen.

References worth reading

• ACVIM consensus guidelines on the diagnosis and treatment of myxomatous mitral valve disease in dogs (the current consensus statement that underpins UK staging and treatment).
• Royal Veterinary College, VetCompass programme, epidemiological studies on canine heart disease in UK primary-care practice.
• BSAVA Manual of Canine and Feline Cardiorespiratory Medicine, current edition.
• Royal College of Veterinary Surgeons (RCVS), Code of Professional Conduct, guidance on euthanasia and end-of-life care.