The long-term of this research is to define the genetic basis of CV diseases in young patients. The goal of this proposal is to identify the gene(s) which cause dilated cardiomyopathy that is transmitted in an autosomal dominant fashion. Cardiomyopathies are defined as "heart muscle diseases of unknown cause." Dilated cardiomyopathy is the most prevalent form of cardiomyopathy, and it is characterized by ventricular dilation with reduced systolic function. By definition, dilated cardiomyopathy is idiopathic, but recent clinical studies have demonstrated a strong genetic component in 20-30% of cases. To find the gene mutation causing dilated cardiomyopathy, l will evaluate three pedigrees using the techniques analysis candidate gene equation and positional cloning. Identification of a genetic cause of dilated cardiomyopathy will enable preclinical diagnosis in individuals at risk, will provide a pathophysiologic basis which may lead to improved therapeutic modalities or prevention, and may improve understanding of heart failure in other cardiac diseases.