RecruitingClinical trialFitness and Lung Function Among Survivors of Heart Transplant, Leukemia and Infant BPD Through ExerciseThis study aims to more accurately assess cardiac function, ventilation and exercise capacity in a non-invasive fashion, and to better characterize exercise intolerance in the setting of three populations of individuals with chronic diseases of childhood (acute lymphoblastic leukemia (ALL), chronic lung disease (CLD) of prematurity, and post-heart transplant (HT))