Inclusion Criteria:

• 1. Age 12-19 years old
• 2. Male or Female
• 3. Diagnosed with one of three congenital heart diseases:
• Univentricular heart with Fontan Palliation Tetralogy of Fallot with transannular patch Dextro-transposition of the great arteries with arterial switch operation
• 4. Primary Cardiology clearance for exercise participation
• 5. Internet access in their homes
• 6. Available for in-home exercise between 4-7pm on at least 3 days of the Monday-Friday work week
• 7. English Speaking
• 8. Achieving maximal effort on a cardiopulmonary exercise test, defined as RER ≥1.1 and/or in the judgement of the supervising exercise physiologist, a maximal effort was achieved but exercise capacity is limited by musculoskeletal deconditioning.

Exclusion Criteria:

• 1. Physically or developmentally unable to perform outcomes assessments or participate in moderate-to-vigorous intensity physical activity
• 2. Participating in \> 15 MET-hours per week (mean weekly average over the past 12- months) of organized athletic/exercise activity (not including school physical education class).
• 3. Height less than 132cm
• 4. Pregnancy or planned surgery or procedure (excluding outpatient, non-cardiac procedures) within the 12-week study period.
• 5. Meeting at least 1 exercise test safety or screening criteria on most recent exercise test (pre-study) or baseline outcomes visit exercise test
• 6. Presence of significant cardiac dysfunction that would impair safe participation in moderate-to-vigorous intensity exercise
• 7. Significant changes baseline echocardiogram or most recent clinical echocardiogram (from past clinical echocardiogram) such as decrease in ventricular and/or valvar function, new obstruction, or any new structural abnormalities
• 8. Uncontrolled or poorly controlled asthma
• 9. Presence of implanted cardioverter-defibrillator
• 10. Pacemaker with rate-responsive function initiated
• 11. Reliance on ventricular assist device
• 12. Prescribed milrinone medication
• 13. Listed for heart transplantation
• 14. Active engagement in hormone replacement for gender transition