What HCM Does to the Heart
Hypertrophic cardiomyopathy, or HCM, is a thickening of the heart muscle that most often affects the wall of the left ventricle. As the muscle thickens the chamber holds less blood and pumps less efficiently, which over time can lead to heart failure, fluid building up in or around the lungs, and dangerous blood clots. It is the most frequently diagnosed heart disease in cats and is seen across many breeds as well as in mixed-breed cats. Some affected cats show no outward signs for years, which is exactly why it is so easy to pass on unknowingly.
Why Ultrasound Is the Gold Standard
The reliable way to assess a cat for HCM is an ultrasound of the heart, called echocardiography, performed by a veterinarian with cardiology training. This scan measures the thickness of the heart walls directly and can reveal changes long before a cat seems unwell. For a handful of breeds, such as the Maine Coon and Ragdoll, validated DNA tests exist for specific mutations, but a normal DNA result does not rule out HCM caused by other factors. For most cats there is no genetic shortcut, so the ultrasound remains essential.
Screen Once, Then Screen Again
A single clear scan in a young cat is reassuring but not a lifetime guarantee, because HCM can develop as a cat grows older. For this reason breeders should screen breeding cats before mating and then repeat the examination on a regular schedule agreed with their veterinarian or cardiologist. A cat that scanned clear at two years old can still develop the disease later and pass it on in the meantime. Regular rescreening is what turns a one-time snapshot into meaningful protection for the whole line.
Using Results Responsibly
Cats that are confirmed to have HCM should not be used for breeding, and close relatives deserve extra attention and monitoring. Share screening results openly with other breeders and with the owners of kittens you place, because transparency is how a breeding community lowers the risk together. Always interpret findings in partnership with a veterinarian who knows the individual cat and its family history. The goal is not a single perfect test but a steady, honest program that keeps healthy hearts in your breeding stock.