HCM (Hypertrophic Cardiomyopathy) in Cats


  • Hypertrophic Cardiomyopathy (HCM) is the most common type of heart disease found in cats.
  • HCM causes the heart muscle to become abnormally thick, which can stop it working properly and lead to heart failure.
  • If it’s caught early, HCM can often be well managed with medication, but, in many cases, it doesn’t cause symptoms (and goes undetected) until it is advanced and severely affecting the rest of the body.

What is HCM (hypertrophic cardiomyopathy)?

Hypertrophic cardiomyopathy (HCM) is the most common type of heart disease found in pet cats. It causes the heart muscle to become abnormally thick, and because of this, the chambers inside the heart get smaller (see image below).

HCM makes it difficult for the heart to pump blood properly, and often leads to:

  • An irregular heartbeat
  • High blood pressure
  • Blood clots (aortic thromboembolism/saddle thrombus) - unfortunately a very common complication of HCM
  • Problems with the heart valves
  • Heart failure (when the heart can’t compensate anymore)
  • Sudden death

What causes HCM?

There are three main types of HCM:

  • Inherited (passed down from a parent) - common in certain breeds.
  • Idiopathic (meaning the cause is unknown).
  • Caused by another condition such as hyperthyroidism or high blood pressure.


HCM often goes undetected for years because it’s a condition that develops gradually. Once symptoms develop (usually at around 5-6 years old), they tend to include:  


If your vet suspects your cat has HCM, they may suggest the following tests:

  • X-rays of the heart and lungs
  • An ultrasound scan of the heart
  • Blood tests to check for raised heart ‘biomarkers’ (a chemical called pro-BNP rises when the heart muscle is damaged or stretched)
  • ECG (a trace of the heart rhythm)
  • Blood pressure measurements


If your cat has HCM, their treatment plan will depend on their how severely they are affected:

Treatment for cats without symptoms - to begin with, if your cat doesn’t have any symptoms, and is at a low risk of complications (such as blood clots), they may not need any treatment. Instead, you will need to monitor them at home, and have them checked by your vet every 6-12 months. They may also need further checks (such as heart scans), to make sure their HCM isn’t getting any worse. Even without symptoms, some cats are at high risk of complications such as blood clots/aortic thromboembolism, and can benefit from anti-clotting medication.

Cats with symptoms - if your cat’s HCM is causing signs and symptoms, they may benefit from heart medication. This is likely to include:

  • Diuretics such as ‘furosemide’ and ‘spirinolactone’. These help remove fluid build-up from the lungs and abdomen (common if the heart is struggling).
  • Inodilators such as ‘pimobendan’, which help the heart pump more effectively.
  • ACE inhibitors such as ‘benazepril’, to make it easier for the heart to pump blood around the body.
  • Anti-coagulants/anti-clotting mediation such as ‘clopridogrel/plavix’ to reduce the risk of blood clots.
  • Beta-blockers to slow the heart rate and help it pump blood more effectively.

Cats with severe symptoms - if your cat has severe symptoms of HCM, such as late-stage heart failure, or a blood clot, they will need emergency treatment from your vet. Sadly, at this stage, they will have a slim chance of survival (especially if they don’t respond to treatment), which means you may need to consider putting them to sleep if they are suffering or in pain.

Home care and monitoring

Breathing rate: if your cat has HCM, one of the most helpful things you can do at home is monitor their ‘resting respiratory rate’/ ‘RRR’ (how many breaths they take each minute while sleeping). Your cat’s RRR should be less than 35 breaths per minute, any higher could be a sign that their heart is struggling to cope. Try to take your cat’s RRR every week, and keep a log of your results. Tell your vet about any rise in your cat’s RRR and show them your log at each check-up.

Body weight: it’s important to keep your cat a healthy bodyweight by feeding them the right amount of a good quality food. Read more about feeding your cat and keeping them the correct weight.

Stress: try to keep your cat as happy and calm as possible by giving them an ideal home and taking steps to prevent stress.

Outlook and life expectancy

It’s very difficult for your vet to predict how long your cat will live with HCM because each case is so different. Although we know that average survival time is 6-9 months once symptoms of heart failure develop, some cats live for many years before developing symptoms, some never develop symptoms, and some sadly, die suddenly without warning.

When to contact your vet

Contact your vet if you are worried about your cat’s heart, or they have any symptoms of HCM. Contact your vet urgently if your cat is struggling to breathe, has collapsed, or has symptoms of an aortic thromboembolism.

Breeds at risk

We know that some breeds of cat are at a higher risk of developing HCM due to their genetics. These breeds include:

There are HCM-testing schemes available, which involve genetic testing and/or regular heart scanning. However, it’s important to be aware that genetic tests aren’t 100% accurate, and many cats with HCM don’t develop any changes that are detectable on ultrasound scan until later in life. Before choosing a cat, it’s important to research the breed to make sure you’re getting a kitten with the best chance at a happy, healthy life.


Treatment for HCM can be very expensive. It’s important to speak openly to your vet about your finances, the cost of treatment, as well as what you think is right for your cat. There is often more than one treatment option, so if one doesn’t work for you and your cat then your vet may be able to offer another.

When you welcome a new cat into your life, consider getting Cat Insurance straight away before any signs of illness start. This will give you peace of mind that you have some financial support if they ever get sick.

Published: April 2021

Written by vets and vet nurses. This advice is for UK pets only. Illustrations by Samantha Elmhurst.