Heart disease in cats: understanding HCM
Cats can hide heart disease; breathing changes require fast action.
Topic illustration selected for this guide. Some learning images may be AI-assisted.This sign can be urgent. Call a veterinarian or emergency clinic now for individual triage; do not wait for this article to diagnose the cause.
Heart disease in cats: understanding HCM — the quick answer
✓ A normal-looking cat can still have HCM
✓ Open-mouth breathing is an emergency
✓ Sudden painful hind-leg weakness is an emergency
✓ A murmur alone neither proves nor excludes HCM
Hypertrophic cardiomyopathy, or HCM, thickens the muscular wall of the heart. Some cats have no outward sign, while others develop breathing difficulty, blood clots or collapse.
Watch breathing, not just energy
A persistent increase in sleeping breathing rate, effort, inability to settle or open-mouth breathing needs veterinary attention. Do not stress a breathless cat with unnecessary handling.
Recognise a possible clot
Sudden crying, dragging or weakness of one or both hind legs, cold paws or severe distress can indicate a clot and requires immediate emergency care.
How vets investigate
Examination, imaging and especially echocardiography may be used depending on findings and risk. Screening advice can differ by breed, age and family history.
Home monitoring
Give prescribed medication consistently and keep follow-up appointments. Ask the clinic how and when to count sleeping breaths and which change should trigger a call.
Your quick checklist
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What to do now
Do not use this guide to delay care. Start with the first step and follow the veterinary professional's instructions.
- 1Learn the cat's sleeping respiratory rate and record a calm baseline.
- 2Give medication exactly as prescribed and keep follow-up imaging or examinations.
- 3Seek emergency care for breathing difficulty, open-mouth breathing, collapse or sudden painful hind-leg weakness.
Common mistakes
×Assuming a normal-looking cat cannot have heart disease.
×Forcing exercise to test stamina.
×Waiting during laboured breathing to count for several hours.
Questions cat people ask
What is HCM in cats?+
Hypertrophic cardiomyopathy is thickening of the heart muscle and is a common feline heart disease. Severity and progression vary greatly.
What breathing rate is dangerous?+
A persistent increase from the individual resting baseline matters. Any effort, open-mouth breathing or distress is an emergency regardless of the number.
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Checked, dated and transparent
- Prepared by
- EverYes Cats editorial team
- Last updated
- 7 August 2026
- Source checked
- 7 August 2026
- Primary reference
- Cornell Feline Health Center: HCM ↗
We begin with the named reference, rewrite the information in plain language and add practical cat-parent steps. Urgent health statements are checked against veterinary sources. This guide has not been individually reviewed by a veterinarian unless explicitly stated. It provides education, not diagnosis or treatment.
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