Phase 3 Triiodothyronine Supplementation for Infants After Cardiopulmonary Bypass

Inclusion Criteria: 1. Informed consent obtained 2. Male and female patients \<5 months (152 days) of age 3. Patients undergoing cardiopulmonary bypass Exclusion Criteria: 1. Known thyroid disease (Down Syndrome is not an exclusion criterion unless patient has thyroid disease) 2. Trisomy 13 and 18 3. Prolonged preoperative ventilator support which would not be impacted by cardiac surgery (Lung disease: bronchopulmonary dysplasia, hypoplastic lungs associated with diaphragmatic hernia) 4. Any other condition as determined by the PI causing prolonged ventilator support which is unlikely to respond favorably to cardiac surgery 5. Prior participation in the clinical trial