The genetic epidemiology study will identify novel dilated cardiomyopathy genes using genetic linkage and mutational analyses. The first aim is to determine the chromosomal location of novel familial dilated cardiomyopathy genes. This will be accomplished by genome-wide genotyping and genetic linkage analyses in three large families with autosomal dominant dilated cardiomyopathy. Previously identified dilated cardiomyopathy genes have been excluded in these families. The second aim is to identify mutations in novel genes that cause familial dilated cardiomyopathy by linkage and sequence analyses of candidate genes mapping to dilated cardiomyopathy loci. Once novel genes for familial dilated cardiomyopathy are identified, the third aim will be to determine the role of these genes in a large cohort of unrelated patients with familial and sporadic dilated cardiomyopathy. High throughput DNA sequence analyses will be performed to identify additional inherited and de novo mutations.