Biomarker Study for Heart Failure in Children With Single Ventricle Physiology

Inclusion Criteria: * Children with a structurally normal heart and a patent ductus arteriosus. * Children with single ventricle physiology. Exclusion Criteria: * Children must not have chromosomal abnormalities. Small deletions, such as that which produces DiGeorge syndrome, are permissible. * Children with acute intercurrent non-cardiac inflammatory illness (such as post-operative wound infection) are ineligible, as such conditions may cause elevated blood levels of the proteins under study.