Hypertrophic cardiomyopathy (HCM) is the most important cause of sudden death in apparently healthy young individuals but its clinical manifestations are highly variable. Linkage analysis is used to localize a gene causing an inherited autosomal dominant disease, such as HCM. Linkage analysis requires that large families be evaluated clinically to determine the members with and without the disease. For this study, DNA needs to be extracted from blood samples of family members. The presence of the disease is determined by history and physical exam, 12 lead ECG and 2-D echocardiogram. The likelihood of localizing the gene increases with the size of the family and the number of members evaluated. The beta myosin heavy chain (beta-MHC) gene has been shown to be responsible for HCM in 10%-30% of affected kindreds. Other linage studies have shown that there are at least 3 other genes which cause HCM in other kindreds, but these genes are presently unknown. We have identified 13 unique mutations in the beta-MHC gene which cause the disease in 17 kindreds. This has allowed us to demonstrate skeletal muscle involvement, study the abnormal physiology which is a consequence of the mutations, make pre-symptomatic diagnosis, and redefine the natural history of the disease. In order to continue our clinical and laboratory studies of this disease over the next 3 years, it is our intention to identify 50 additional HCM kindreds, with approximately 50 members each, that have beta-MHC gene mutations. During this time, in order to map other HCM genes, we will also evaluate at least 6 families, of approximately 300 members each, in which the disease is not linked to the beta-MHC gene.