Cardiomyopathy in children is a serious disease which can result in death, disability, heart transplantation or serious heart rhythm disorders. Doctors know little about the causes of cardiomyopathy but would like to learn more. In fact, up to 50-75% of cases in children have no known cause. For this reason, the purpose of this study is to identify genes that cause cardiomyopathy or that influence how people with cardiomyopathy do over time. These findings could improve disease prevention, surveillance, early management, and prognosis.