Your cat may seem perfectly healthy, but sometimes serious health problems can be hiding beneath the surface. Hypertrophic cardiomyopathy (HCM) is one of the most common feline heart diseases — and here's the scary part: most cats don't show any symptoms until it's too late to intervene. As a cat parent, you might not know anything's wrong until it becomes urgent. But here's the good news: A simple yearly vet visit could make a difference.