Cardiomyopathy is an important cause of chronic disability and death in pediatric patients and currently accounts for approximately 50% of cardiac transplants performed during childhood. Left ventricular (LV) size and function are important independent predictors of outcome, and echocardiography is the primary way to assess ventricular function in children. Although there is extensive experience with this technology, data are limited on how ventricular function changes over time in children, which is a major impediment to conducting controlled trials of therapy in children.