Feline hypertrophic cardiomyopathy (HCM) is the most common cause of heart disease in the adult cat. Affected cats are at risk of sudden death, breathing difficulties or development of a blood clot. Increasingly, feline HCM is noted to be inherited, with examples reported in the Maine Coon, Ragdoll, British shorthair, and Scottish Fold breeds, among others. We demonstrated that HCM is associated with a mutation in the myosin binding protein C gene in the Maine Coon cat. In human beings, the disease is commonly associated with a mutation in one of several genes that encode for sarcomeric proteins, most commonly the myosin binding protein C and the beta myosin heavy chain gene. Causative mutations have been identified in over 140 regions of the cardiac myosin binding protein C gene alone. The Ragdoll cat also has a heritable form of the disease. We prospectively collected pedigrees and medical information and DNA samples from 3 families of Ragdoll cats with familial HCM. We performed an initial study of affected Ragdoll cats and determined that the Maine Coon defect is not present. However, we only evaluated one small region of the gene. Given the importance of this gene in both humans and Maine Coon cats with HCM we hypothesize that a mutation in a different region of the gene is associated with the development HCM in the Ragdoll. The objective of this study is to evaluate the DNA of this gene in both affected and unaffected cats for a causative mutation.