Venous Compression in Fontan

Study Day 1 - Consent, Screening and Garment Measurements: Following assessment of participant eligibility, all participants will undergo leg venous ultrasound assessment and abdominal-foot measurements for the custom making of compression garments. Study Day 2 - MRI: Study participants will undergo comprehensive cardiovascular MRI using a 3T MRI scanner with and without compression garments and exercise. Study Day 3 - Cardiovascular \& Exercise Testing Day: All participants will undergo comprehensive cardiovascular structure and function assessments at rest and during exercise with and without the wearing of compression garments. Baseline testing will include dual x-ray absorptiometry (DEXA), pulmonary function testing, comprensive vascular assessments and echocardiography. During exercise at two submaximal workloads, the study team will measure blood pressure, oxygen uptake and cardiac output.