Breed Health Guide • Reviewed by Dr. Tiffany Delacruz, DVM
Hypertrophic Cardiomyopathy in Maine Coons
Also known as: HCM
Hypertrophic Cardiomyopathy (HCM) is the most common heart disease in cats and the leading cause of sudden death in Maine Coons. The heart muscle thickens, the chamber holds less blood, and over time the cat can develop heart failure or a fatal blood clot. Maine Coons have a well-characterized inherited form linked to the MyBPC3 (A31P) mutation.
Why Maine Coons are predisposed to hypertrophic cardiomyopathy
Maine Coons carry a specific mutation in the cardiac myosin binding protein C gene (MyBPC3, A31P) that significantly increases HCM risk. The mutation is autosomal dominant with incomplete penetrance — cats with one copy can develop disease, cats with two copies are at very high risk, and even cats with no copies of A31P can still develop HCM from other unidentified mutations. Genetic testing is widely available and used in responsible breeding programs to reduce disease frequency in the breed.
What you'll see at home
- Often nothing visible early — HCM is silent in the pre-clinical phase
- Heart murmur on routine vet exam (often the first sign)
- Hiding more, reduced activity, sleeping more
- Increased resting respiratory rate (>30 breaths/min while sleeping)
- Open-mouth breathing or panting (urgent — cats rarely pant)
- Sudden hind-limb paralysis or severe pain (aortic thromboembolism — saddle thrombus)
- Collapse or fainting
- Sudden cardiac death (sometimes the first sign)
Red flags — go to an emergency vet
- ⚠ Open-mouth breathing or labored breathing — cats almost never breathe through their mouth unless in severe respiratory distress (ER now)
- ⚠ Sudden hind-leg paralysis or screaming with pain in the back end — aortic thromboembolism (saddle thrombus) is excruciating and time-critical
- ⚠ Resting respiratory rate over 40/min while sleeping
- ⚠ Collapse or fainting
- ⚠ Pale, blue, or grey gums
How vets diagnose hypertrophic cardiomyopathy
Annual cardiac auscultation from kittenhood — vets listen for HCM-related murmurs and gallop sounds. Echocardiogram (echo) by a board-certified cardiologist is the gold standard — measures wall thickness, chamber size, and left atrial enlargement. Genetic testing (MyBPC3 A31P) identifies high-risk cats but does NOT replace echo screening (gene-negative cats can still have HCM). NT-proBNP blood test is a useful screening tool.
Treatment options
Pre-clinical (stage B) HCM without atrial enlargement — no medication is needed in most cases; monitor every 6-12 months. Stage B2 with left atrial enlargement — atenolol or anti-clotting drugs (clopidogrel) are commonly added to reduce thromboembolism risk. Stage C (clinical heart failure) — furosemide (diuretic), pimobendan, ACE inhibitors, clopidogrel. Stage D — refractory, multi-drug regimens. New drug Solensia (frunevetmab) and Cardalis are not for HCM but the field is evolving.
Common medications for this condition
Don't start, stop, or change any of these medications without a licensed vet's guidance.
Living with a Maine Coon who has hypertrophic cardiomyopathy
- 1 Cardiac auscultation at every annual vet visit from kittenhood
- 2 Echo screening at age 1, then every 1-2 years for at-risk breeds
- 3 MyBPC3 A31P genetic test once in a lifetime
- 4 Monitor sleeping respiratory rate at home — count breaths/min when fully asleep; over 30 is a warning sign
- 5 Keep your Maine Coon lean — extra weight increases cardiac workload
- 6 Indoor only to reduce stress and stranger encounters that can precipitate decompensation
- 7 Give medications exactly as prescribed — missed atenolol or clopidogrel doses raise clot risk
- 8 Avoid stressful events (travel, boarding) without veterinary guidance for cats with known HCM
Can RexVet help with this online?
A RexVet video visit is excellent for: atenolol, clopidogrel, furosemide, and pimobendan refills for an already-staged Maine Coon, monthly check-ins on respiratory rate and energy, side-effect management, weight management, and helping you decide whether new symptoms warrant urgent in-person cardiology follow-up.
Start a $64.99 video visit →We can't perform echocardiograms, chest x-rays, or genetic testing by video — those need an in-person veterinary cardiologist. Acute decompensation (open-mouth breathing, saddle thrombus, collapse) is an ER situation requiring oxygen, IV diuretics, and emergency stabilization.
Prognosis — what to expect
Highly variable. Many Maine Coons with mild HCM live near-normal lifespans with good monitoring. Once a cat develops left atrial enlargement, the risk of saddle thrombus and heart failure climbs sharply. Cats that develop clinical heart failure have a median survival of 12-18 months with aggressive treatment. Cats that suffer a saddle thrombus have much shorter survival — many are euthanized at the time of the event. Early genetic screening and echo monitoring is the most important lever for the breed.
Frequently asked questions
Frequently asked questions
How can I tell if my Maine Coon has HCM?
Most cats with early HCM show no symptoms — the disease is silent until significant. A heart murmur on a routine vet exam is often the first clue, but many HCM cats don't have a murmur. Echocardiogram by a cardiologist is the definitive test. Genetic testing for MyBPC3 A31P identifies high-risk cats. If your Maine Coon has any open-mouth breathing or sudden hindlimb weakness, treat it as an emergency.
Should I genetic test my Maine Coon for HCM?
Yes — MyBPC3 A31P testing is inexpensive (typically under $100), works at any age, and identifies cats at high inherited risk. Cats with two copies of A31P develop HCM at high rates; cats with one copy have intermediate risk. Important: a negative MyBPC3 test does not rule out HCM. Echo screening from age 1+ is still recommended for all Maine Coons.
Is HCM hereditary in Maine Coons?
Yes — the MyBPC3 A31P mutation is autosomal dominant with incomplete penetrance. The mutation is widespread in the breed, though responsible breeders have reduced its frequency through testing. Even cats from tested lines can develop HCM from other (currently unidentified) genetic causes, so screening matters regardless of pedigree.
How long can a Maine Coon live with HCM?
Pre-clinical HCM with no left atrial enlargement — many cats live full normal lifespans. Cats with left atrial enlargement on echo have higher risk of thromboembolism and heart failure. Cats in clinical congestive heart failure have a median survival of 12-18 months with current multi-drug therapy. Sudden cardiac death and saddle thrombus are the two most feared outcomes — both are unpredictable in many cases.
Further reading from the RexVet blog
Sources
- ACVIM Consensus Statement on Feline Cardiomyopathy
- Cornell — Feline HCM
- Winn Feline Foundation — HCM Research
Last fact-checked: 2026-06-01. Reviewed by Dr. Tiffany Delacruz, DVM.
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