Over 100,000 Canadian children are living with congenital heart defects and approximately 1.5% of them have a univentricular heart. The Fontan procedure allows children with functionally univentricular hearts to live relatively normal lives. However, the cardiopulmonary physiology remains abnormal and chronic complications, including myocardial dysfunction, arrhythmias, pathway abnormalities, hepatic dysfunction, obstruction of the ventricular outflow tract or pulmonary veins, and pulmonary arteriovenous malformations may significantly reduce maximal exercise capacity and quality of life. Quality of life and life-long heart health are, therefore, critically important for Fontan patients as their survival depends on the continued functioning of an already sub-normal cardiopulmonary physiology.