While there is very little data available regarding the causes of failure in children with single ventricle anatomy, it is clear that genetic factors which influence ventricular function and the development of heart failure in adults with two ventricles could play a role in the failure of patients with one ventricle. We propose a combined retrospective and prospective evaluation of each of the candidate gene polymorphisms discussed above for potential linkage to poor outcome in children with single ventricle anatomy. Poor outcome for these children would be defined as a multi-endpoint variable including death, evaluation for heart transplantation, or the development of severe single ventricle dysfunction by echocardiographic or cardiac catheterization criteria. Identification of high-risk combinations of genetic alleles could guide therapy for patients with poor predicted outcome, possibly steering such patients towards early transplantation rather than attempted staged palliation.