Objective: Our primary objective is to determine if early institution of PD improves clinical outcomes compared to administration of furosemide in post-operative cardiac infants with acute kidney injury. We hypothesize that early initiation of PD will improve clinical outcomes. We will determine if these clinical outcomes will be better among good responders of furosemide compared to poor responders. We will determine if postoperative NGAL concentrations are predictive of poor response to furosemide.