The purpose of this protocol is to measure the relaxation of the heart in subjects with single ventricles who have undergone the surgical Fontan procedure. We will do this by measuring relaxation with MRI, echocardiography, and cardiac catheterization and compare to blood levels that measure heart scarring. We will also measure relaxation before and after boluses of intravenous (IV) fluids to see if the relaxation changes when there is more fluid in the heart. Measurements of heart relaxation will be obtained from the MRI, echocardiogram, and cardiac catheterization for each patient and compared to blood markers of heart scarring. We aim to compare all of these measurements to see if we can accurately identify heart scarring and, if present, how much it correlates with impaired heart relaxation.

Inclusion criteria: adult patients (age ≥18) with a previous Fontan procedure (including all variants) referred for catheterization. This includes individuals with tricuspid atresia, double inlet left ventricle, unbalanced atrioventricular septal defect, and pulmonary atresia with intact septum. Control subjects will be selected from individuals referred to the lab for evaluation/closure of a patent foramen ovale (PFO). All subjects must be willing to participate in all portions of the study and provide written informed consent.

Exclusion criteria: contraindications to MRI such as ferromagnetic objects in the chest, claustrophobia, or contraindication to gadolinium contrast (estimated creatinine clearance < 30 ml/min/1.73m2). Fontan patients with a morphologic right ventricle (namely hypoplastic left heart after a Norwood palliation) will be excluded, because of the disproportionate risk of systolic dysfunction in the morphologic right ventricle.33 Control patients with hypertension, diabetes, coronary disease, or reduced systolic function will be excluded.

Patients with a single ventricle palliated with a Fontan procedure