IMProving DRug Dosing and Outcomes for Single VEntricle Patients With Fontan Associated Liver Disease

This is a single center, open-label, prospective, investigation to quantify the effects liver congestion and fibrosis has on hepatic drug metabolism and transport in children, adolescents, and young adults with Fontan circulation.

Inclusion Criteria: * \> 8 years * Status Post Fontan Completion * Ability to provide informed permission-assent (\5X the age-specific upper limit of normal for aspartate aminotransferase (AST) and alanine aminotransferase (ALT), total and conjugated bilirubin * Diarrhea in the last 24 hours \*History of solid organ transplantation