Hypertrophic Cardiomyopathy
HCM is the most common heart disease in cats, and the Maine Coon is one of the breeds most affected by it. It is also the single condition buyers ask us about most often — so here is what it is, what it does, and exactly what our testing does and does not rule out.
What it is
In a healthy heart the muscular wall of the left ventricle stays thin enough to relax and fill with blood between beats. In hypertrophic cardiomyopathy that wall thickens. The chamber holds less, the muscle stiffens, and the heart has to work harder to move less blood.
In Maine Coons a specific inherited mutation in the MYBPC3 gene — usually written A31P — is strongly associated with the disease. That mutation is what a Maine Coon HCM DNA test looks for.
Why it matters
HCM is dangerous because it is quiet. A cat can carry a thickened heart for years and behave completely normally: eating, playing, showing nothing an owner could reasonably spot.
When it does surface it tends to surface badly — congestive heart failure, or a clot that lodges where the aorta divides and paralyses the hind legs suddenly and painfully, or sudden death in a cat that seemed healthy the day before. This is why it is screened for before breeding rather than watched for afterwards.
How it affects Maine Coons
The breed is over-represented in every survey of feline HCM. The A31P mutation behaves dominantly, which means one copy is enough to raise a cat's risk — unlike the recessive conditions on this page, there is no such thing as a silent carrier that is safe to breed from.
One honest caveat, because it matters more than any marketing line: not all HCM in the breed comes from this mutation. A cat can test genetically clear and still develop HCM from another cause. A clear DNA result removes the known inherited form — the form that can be predicted and bred away from. Any breeder who tells you a DNA test guarantees a heart-healthy cat for life is overselling it.
How we prevent it
Every King and Queen is DNA tested before entering our program, and we do not breed from a cat carrying the mutation. Because the parents are cleared before mating, every kitten is cleared by parentage for the inherited form.
Our testing is run by Langford Vets at the University of Bristol, and the report for each cat is issued against that individual animal's microchip and registration number. You can see one of those reports in full on our genetic testing page.