Cholate Clearance in Fontan and Heart Failure

Inclusion Criteria: * Fontan: Adult Fontan patients ≥ 18 years of age who have undergone right heart catheterization within the past 1 year. * RHF Controls: non-Fontan adults with two ventricle anatomy with systemic left ventricle, CVP estimate ≥ 8 mmHg and left ventricle (LV) function ≥ 50% by echocardiogram performed within the past 1 year. Can include those with congenital heart disease- repaired or unrepaired. * Normal Controls: non-Fontan adults with normal cardiac anatomy, normal biventricular function, \< moderate tricuspid regurgitation and CVP estimate \< 5 mmHg by echocardiogram performed within the past 1 year. Exclusion Criteria: * Pregnant or breastfeeding * Unable to comprehend and/or give informed consent * Sensitivity to human serum albumin, or its preparations * Participants with extensive resection of large segments of the small intestine (short gut) or severe gastroparesis * Participants on non-selective beta blockers, angiotensin converting-enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), ursodeoxycholic acid, cholic acid, or other bile acids who are unwilling or unable to delay taking their normal dose the morning of their dual cholate clearance testing. * Participants on dietary supplements, bile acid sequestrants, GLP-1 agonists, narcotics, and other medications affecting gastric emptying or intestinal absorption who are unwilling or unable to delay taking or withhold as outlined in the instructions on deviating from the SHUNT test. * Contraindication to cardiac MRI * For RHF and normal controls: diabetes, chronic liver disease, \>moderate alcohol use, BMI \>30, oxygen-dependent, pulmonary hypertension22 on therapy, known porto-pulmonary hypertension