Hypertrophic cardiomyopathy (HCM) is a disease of the heart muscle characterized by thickening of the left ventricular walls. The disease may result in heart failure, thromboembolism, and sudden death. The disease in humans is frequently caused by an inherited defect in the gene of a cardiac contractile protein. Clinically, the characteristics of feline HCM are very similar to that in humans with genetic HCM. These findings support the hypotheses that feline HCM is inherited and may be caused by mutations in contractile protein genes. In previous Winn-funded studies, the investigators examined several suspect genes for mutations in several groups of related cats. No abnormalities were identified. Currently, the investigators are closely examining the myosin binding protein C that preliminarily appears to be abnormal in Maine Coons. If mutations are identified, genetic tests will be formulated to easily and rapidly detect these mutations. This is a continuation of a grant first awarded in 1995.