This study's objective is to determine the pharmacokinetics (PK)/pharmacodynamics (PD), safety and efficacy of methylprednisolone in infants undergoing heart surgery with cardiopulmonary bypass. This is a prospective, double blind, multi-center, placebo-controlled safety and efficacy study. Blood samples will be collected from a subset of enrolled study participants to evaluate multiple dose methylprednisolone PK/PD. Participants will be randomized in a 1:1 fashion to intravenous methylprednisolone versus placebo. Study drug/placebo will be administered 8 to 12 hours before the anticipated start time of surgery and in the operating room at the time of initiation of cardiopulmonary bypass. Patients will be followed for primary and secondary outcomes for the duration of their hospitalization. Serious study drug-related adverse events will be collected for 7 days after the last dose of study drug.