Single ventricle patients will be recruited from the cohort of patients treated and/or followed at The Children's Hospital of Philadelphia in the cardiology program and surrounding hospitals/institutions. In specific, patients will be approached to participate in the study during clinic visits or visits to the hospital for other reasons. Children for the normal control group will be recruited from children who are undergoing clinical MRIs at CHOP. A full understanding of all study related procedures and processes will be explained to the subject, including all MRI scans, how the MRI scanner works and how the proposed research will help medical practice. Children likely to have a normal brain MRI will be asked to participate and sign an informed consent form.