This is a single center prospective longitudinal exercise training 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.

Participants will undergo an MRI of the Fontan circulation. This will include imaging of the heart, lung and liver. This will include specific imaging for tissue characterization and assessment of myocardial fibrosis, liver fibrosis and disproportionate pulmonary blood flow. The investigators will then draw blood (approximately 10 ml) for assessment of serum biomarkers and circulating microRNAs of interest. The participants will undergo exercise testing and will then start a 3-6 month long cardiac rehabilitation program. After the 3-6 month study period the participants will return back for a follow up and repeat all the testing completed at enrollement.

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.

Participants will receive an MRI of the Fontan circulation. This will include imaging of the heart, lung and liver. A blood draw (approximately 10 ml) for assessment of serum biomarkers and circulating microRNAs of interest will be completed. The participants will also complete exercise testing and will then start a 3-6 month long cardiac rehabilitation program. Frequent phone follow up (conducted by the research staff) and regular download of data from heart rate monitors will ensure adherence.

After the 3-6 month study period the participants will return for a follow up and repeat all testing completed at enrollment.

Inclusion Criteria:

• Presence of a congenital heart defect that leads to single ventricle physiology
• Previously performed TCPA surgery
• Current age 10 years to 40 years
• Informed consent

Exclusion Criteria:

• History of exercise intolerance (peak VO2<12ml/kg/min)
• Unstable arrhythmia at the time of screening
• Listed or being evaluated for heart transplantation
• Pregnancy or breast feeding
• Patient with pacemaker, AV block other than 1st degree block, sick sinus syndrome or other arrhythmia that may influence ability to perform exercise test or magnetic resonance imaging