RecruitingDiagnostic testExercise MRI to Evaluate Cardiorespiratory Fitness in Children With Heart DiseaseThere are many barriers to heart-healthy lifestyles in pediatric patients with acquired and congenital heart disease. Investigators want to further understand how participants heart and skeletal muscles work together during exercise and evaluate the impact on cardiac function. To do this, the investigators will use magnetic resonance imaging (MRI) to scan the heart and skeletal muscles during exercises to assess blood flow, oxygenation and function.