One in 3,000 children is born with one, instead of two, heart pumps, and as a result of a surgery called the “Fontan”, survive well into into adulthood. This surgery creates an artificial path that collects blood low in oxygen from the veins and sends to the lungs (instead of using a right heart pump) to pick up oxygen; leaving the single pump to send blood with oxygen to the body. We are learning these patients are developing many issues in adulthood including liver disease. The best way of identifying significant liver disease is through a liver biopsy, but it is not reasonable to perform biopsies regularly. We do not know the best way to easily identify and monitor liver disease in the Fontan population, yet this knowledge is critical to maintaining Fontan liver health, reducing co-morbidities ultimately benefiting our health care system. The first part of the study will be undertaken at St.Paul’s Hospital and Mazankowski Heart Center in Edmonton. We will perform a number of liver related blood tests/imaging to determine the best combination that identifies significant liver disease as diagnosed by liver biopsy. The second part will take place at five adult sites across Canada and will confirm our findings from the first part.