RecruitingDevice studyCholate Clearance in Fontan and Heart FailureThe goal of this study is to use the HepQuant dual cholate clearance assay, which has been shown to measure liver function in people with known chronic liver conditions, to assess severity of Fontan-associated liver disease (FALD). This study aims to understand the role impaired blood flow to the liver plays in liver function in Fontan patients compared to patients with right heart failure and healthy controls. The study will also determine whether cholate clearance is a good measure to use in this population, and whether it will be able to predict clinical outcomes. Participants will undergo a HepQuant dual cholate clearance assay and a cardiac magnetic resonance imaging (MRI) at the beginning of the study, and then data on health status will be collected for 5 years.