u/ailurophile17 The vet can check for the heart murmur at a regular visit. This is what the vets always listen for at all visits for any animal. If the vet can detect heart murmur, they perform echocardiogram study to evaluate it further. If you went for vet visits to have your cat vaccinated over the years, and the vet did not detect heart murmur at any of the visits, then your cat did not die from HCM. HCM is not the same as heart attack in people. I work at the vet office. You said that Pixel was healthy and died suddenly at 7 years old. Your Pixel did not die from HCM. You should have done an autopsy to find the actual cause of Pixel's death.