Specific hypotheses are that l) during the period of the registry, the percentage of cases that are diagnosed as idiopathic will decrease (i.e., etiologies will be found) and 2) at the time of diagnosis of cardiomyopathy, factors such as gender, ethnicity, age, type of cardiomyopathy, and presence or absence of a syndrome can help predict outcomes. Definition of entry and exclusion criteria, clinical quality assurance, and accrual and retention of participating clinical centers are largely under the direction of the University of Rochester in Rochester, New York and Baylor College of Medicine. Virtually all pediatric cardiology centers in the United States, Puerto Rico, and Canada have expressed their willingness to send patient information to such a registry.