Heart murmurs in dogs and cats

10 February 2022 - 6 min read
Vet listening to a cat's heart

If you’ve been told your cat or dog has a heart murmur, you might be wondering how worried you should be.

Vet Sophie Bell cuts through the jargon to help you understand how your pet’s heart murmur might impact their life, what you can do to take care of them and whether their treatment will be covered by your pet insurance.

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What is a heart murmur?

“A heart murmur is an abnormal sound heard when the heart is listened to using a stethoscope, say’s Sophie. “It makes a whooshing sound instead of a clear beat. This is due to turbulent blood flow.”

Although the heart murmur itself is a symptom rather than a disease, it can be a sign that something else is wrong.

“It’s not always a sign of heart disease or a sign that your dog is suffering with any other disease, but it does need investigating to find out what’s causing it,” says Sophie.

What causes a heart murmur?

In both dogs and cats “a heart murmur can be caused by any condition – whether intracardiac or extracardiac – that causes turbulent blood flow through the heart,” says Sophie.

‘Intracardiac’ means something inside the heart and ‘extracardiac’ means (yes, you’ve guessed it) something outside the heart.

Intracardiac causes are basically those caused by heart disease and extracardiac causes are those not caused by heart disease,” says Sophie.

That means a heart murmur could be caused by something very benign, for example large breed puppies will sometimes have a heart murmur while they’re growing very quickly. But it could also be a symptom of a much more serious condition, like heart disease caused by a structural problem with the heart.

Although extracardiac causes of heart murmurs in dogs and cats aren’t necessarily less serious than intracardiac ones, “technically once the issue has been resolved the murmur should also resolve,” says Sophie.

Extracardiac causes of heart murmurs

These causes might in themselves be symptoms of another disease or condition:

  • Anaemia

  • Infection and fever

  • Obesity

  • Emaciation

  • Low blood protein

Intracardiac causes of heart murmurs

These are due to cardiac disease and include:

  • Diseased heart valves

  • Thickened chambers

  • Hereditary heart disease

  • Hypertrophic cardiomyopathy caused by Hyperthyroidism (in cats)

Problems with the heart itself that cause a heart murmur may be hereditary. For example, a condition called aortic stenosis is sometimes seen in some large breeds like Newfoundlands or Rottweilers.

Grades of heart murmur for dogs and cats

Your vet will give your dog or cat’s heart murmur a grade between one-six. This simply relates to its volume, with a grade one heart murmur being the quietest and a grade six the loudest.

So you might assume that the higher the grade, the more serious the problem. But that’s not always the case, says vet Sophie.

“For grade six there will simply be a higher amount of blood turbulence as it flows through the heart. Although the louder the murmur the possible likelihood of higher severity disease, that isn’t always the case.”

So you can’t just say a dog with a grade two or three heart murmur is less serious than a dog with a grade four murmur – it simply means it’s quieter.

Murmurs are also classified by where they are heard – the left side of the chest, the right side, or all over.

Finally, they’re classified by when they occur. For example during systole (when blood is pumped out) or diastole (when the heart is refilling). “Most are during systole,” says Sophie.

Diagnosing heart murmurs in cats and dogs

Although your vet can spot and grade your pet’s heart murmur using a stethoscope, how they find and diagnose the cause will depend on your pet’s history and symptoms and what’s found on clinical exam.

Diagnostic techniques could include blood tests, x-rays, ultrasound or an echocardiogram (ECG).

Vet listening to a dog's heart

Heart murmurs in dogs

Lots of dogs have a heart murmur and it isn’t always something to worry about. But heart disease is more common in older dogs – “30% of senior dogs suffer with degenerative mitral valve disease that causes a murmur,” says Sophie.

Symptoms of a heart murmur in dogs

Your vet needs to listen to your dog’s chest with a stethoscope to hear their heart murmur. You won’t be able to hear it yourself.

High-grade heart murmurs (five and six) can cause strong vibrations in the heart. “You may be able to feel it when you place your hand on your dog’s chest, this is called a thrill,” says Sophie.

Because a heart murmur can itself be a symptom of heart disease, it may be seen alongside other heart disease symptoms, including:

  • Coughing

  • Exercise intolerance

  • Loss of appetite

  • Weight loss

  • Pale (grey or blue) gums

  • Weakness, lethargy tiredness

  • Breathing problems, e.g. too rapid, noisy, laboured

“The normal resting respiratory rate for a dog is 10-30 breaths per minute, says Sophie. Breathing should be free and easy, heart disease can cause laboured rapid breathing.”

Dog heart murmur treatments

Cost of a work-up to find the causes of a heart murmur will vary from one vet to another and depending on what needs to be done.

“If a heart murmur was detected and the dog had a form of autoimmune haemolytic anaemia treating the underlying disease could cost thousands,” says Vet Sophie. “I saw one at vet school whose final bill was £24,000”

Thankfully, many dogs will cost a lot less to treat. In 2021, heart murmurs were the most common type of cardiac claim we dealt with in dogs. There were 887 claims for a heart murmur, costing £394.79 on average.

“The minimum cost to manage heart disease could range from cheap diuretics like furosemide that cost as little as 14p per day if you source your drugs using a prescription, up to say £3-£4 per day. It depends on the problem, says Sophie.

For some heart conditions surgery may be an option, which is considerably more expensive.

Life expectancy for a dog with a heart murmur

Because a heart murmur has so many causes, don’t immediately assume your dog’s life will be shortened.

“Until you know why your dog has a murmur, then don’t worry unnecessarily but I also would not just leave it,” says Sophie. “Your vet will perform a ‘work-up’ including bloods and an ultrasound scan to find out the reason for the murmur and whether your dog will require further treatment or not.”

So are heart murmurs dangerous in dogs?

“Yes, they can be, hence why further investigations to determine the cause are important. But a murmur is not always related to heart disease,” says Sophie.

Some murmurs  are labelled as innocent murmurs and may well go away on their own. They won’t reduce your dog’s life expectancy.

“Rapidly growing large breed puppies are one example where a murmur may be picked up around two months of age and gone by five months of age, says Sophie. “Another example is an anaemic puppy due to something such as fleas. Once the anaemia is addressed the murmur will disappear.

“In this case the animal requires treatment, so it won’t go away on its own but will go away, unlike murmurs caused by heart disease which remain audible despite managing the heart disease with medication.

Heart murmurs in cats

Heart murmurs in cats are very common. Vet Sophie says that the most recent studies show more than a third of cats have one.

Symptoms of heart murmur in cats

A lot of the symptoms are the same as for dogs and again are associated with heart conditions:

  • Coughing

  • Lethargy and tiredness

  • Loss of appetite

  • Weight loss

  • Pale gums

  • Breathing problems

A healthy cat should take cat should take 20-30 breaths per minute.

One other symptom that might be seen in cats is sudden onset of hindlimb paralysis. This may be caused by thromboembolism or saddle thrombus, which is a blood clot. It comes on very suddenly and unfortunately the prognosis is very poor.

Cat heart murmur treatments

Again, the diagnostics and treatment will be similar for dogs.  Your vet will be looking for a cause of your cat’s heart murmur so may do blood tests, an ultrasound or other tests.

Although the medication might be the same, it’s likely to cost a bit less to treat a cat for heart disease than a dog, simply because they’re smaller so will need a lower dose of heart murmur medication.

In 2021, we saw 224 cat heart murmur claims, with an average cost of £362.27.

The average cost of a claim for thromboembolism, one of the causes of heart murmurs in cats, was £913.44.

Life expectancy for a cat with a heart murmur

Your cat’s heart murmur might be innocent or caused by a mild condition, in which case it may not shorten their life at all. Lots of cats live with a heart murmur for their entire life.

But cats can hide other symptoms well and can go downhill quickly, so a heart murmur should be investigated by your vet.

This is especially true for older cats who develop a heart murmur that they didn’t have when they were younger.

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Can I insure my dog or cat with a with a heart murmur?

If your pet’s already insured, a newly detected heart murmur should be covered by your pet insurance. But if your cat or dog already has a murmur and you switch insurers or take out pet insurance for the first time, it may be classes as a pre-existing condition.

Most pet insurance policies don’t cover previous conditions, but all our policies cover conditions that ended over two years ago. So if your dog or cat previously had a murmur that's resolved and has had no treatment, medication or advice for two years, we could cover a new murmur.

We also have a Pre-existing policy that could potentially cover a more recent murmur, as long as it's had no treatment, medication or advice from your vet in the three months before you take out the policy.

Caring for pets with a heart murmur

Whatever the cause of your cat or dog’s heart murmur, you can take some practical steps at home to keep their heart healthy.

Control their weight – weigh out their food every time, don’t just guess. And don’t forget to allow for any treats and reduce their meal sizes accordingly. Make sure they get the right amount and right type of exercise as well, following your vet’s advice.

Omega 3 and 6 – Omegas in supplements and fish oils have a raft of health benefits, including boosting heart health.

Regular vet checks – Once it’s been diagnosed, your vet can monitor your pet’s heart murmur and any conditions that cause it at regular visits

Avoid breeding – If your dog’s heart problems are hereditary, it’s best not to breed from them to avoid passing the health problems on to their puppies.


Derri Dunn
Content marketer

Derri is a personal finance and insurance writer and editor. After seven years covering all things motoring and banking at GoCompare, Derri joined ManyPets in 2021 to focus on pet health. She has fostered cats and kittens for Blue Cross and Cats Protection and is owned by tabby cat Diggory and two badly behaved dogs.