This is a single center prospective longitudinal study and will enroll approximately 50 Fontan patients and 20 controls of a similar age, gender, BMI and physical activity level between the ages of 10-40 years. The investigators will enroll from pediatric cardiology and heart failure clinics and inpatient care units at Children's Health Dallas, adult congenital heart disease clinics and inpatient care units at Clements University Hospital and the Clinical Heart Center. This study will evaluate the multimodality biomarkers for assessment of Fontan circulation including heart, liver and lung and change in these markers with exercise training.