Hypertrophic cardiomyopathy in cats – signs and care

Updated 2026-09-30 · 2 sources

Based on: PDSA, Science for Animal Welfare (UFAW), Genetic Welfare Problems of Companion Animals

Contact a vet today

Contact your vet today if you think your cat has this – it can become serious. It is a condition where the heart muscle becomes abnormally thick.

What to do now

What you can do now

Contact your vet today if you think your cat has this.
Contact your vet urgently if your cat is struggling to breathe, has collapsed, or has symptoms of an aortic thromboembolism.
Note when it started, how often it happens and what else you see.
Take a photo or short video to show the vet.
Let your cat rest somewhere calm.

Don't

Do not give any human medicine.
Do not wait if it gets worse.

What it is

Hypertrophic cardiomyopathy is a condition in which the heart muscle becomes abnormally thick.^[1] It can stop the heart working properly and lead to heart failure.^[1]

Signs

Low energy
Breathlessness or sudden difficulty breathing
Fainting or collapse
Eating less or not eating
A fast, ‘galloping’ heart rate
A heart murmur, which is not always present
Paralysis in one or both back legs due to an aortic thromboembolism or saddle thrombus
Sudden death

gradual

Causes and risk factors

Inherited, passed down from a parent
Idiopathic, meaning the cause is unknown
Another condition such as hyperthyroidism or high blood pressure
Maine Coon
Persian
Ragdoll
Bengal
British Shorthair
Norwegian Forest Cat

How a vet finds out

Blood tests
X-rays
Ultrasound
ECG
Blood pressure measurement

How vets treat it

Medication
A cat without symptoms and at low risk of complications may not need treatment to begin with

Breeds prone to this

Veterinary charities list these breeds as more likely than others to get this condition. Each breed page lists the inherited conditions documented in the breed.

What the experts say

“Overview. 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.”
— PDSA [1]

If your pet is struggling to breathe, has collapsed, is having a seizure or can't stand up: go to the nearest vet now.

Not sure how serious it is?

OkPaw asks a few quick questions about your pet and tells you in 30 seconds whether it can wait. Free on Google Play for Android.

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Common questions

What is hypertrophic cardiomyopathy?

It causes the heart muscle to become abnormally thick, which can stop it working properly and lead to heart failure.^[1]

What signs can it cause?

Signs can include low energy, breathlessness or sudden difficulty breathing, fainting or collapse, eating less or not eating, a fast ‘galloping’ heart rate, a heart murmur that is not always present, paralysis in one or both back legs due to an aortic thromboembolism or saddle thrombus, and sudden death.^[1]

When should I contact a vet urgently?

If your cat is struggling to breathe, has collapsed, or has symptoms of an aortic thromboembolism, contact your vet urgently.^[1]

Sources

How this page was made: written with the help of AI from the sources below, then checked claim by claim against those sources. Urgency levels follow OkPaw’s fixed safety rules. It is guidance, not a diagnosis. How we write our pages