This is a Phase 1, randomized, double-blind, dose escalation, safety and pharmacokinetic study. The study will be conducted in approximately 8-10 centers in the United States and Switzerland. Up to 32 patients who have undergone major cardiovascular surgery will participate. Patients will receive a single IV injection of I5NP or placebo following cardiovascular surgery. I5NP will be administered 4 hours (+/- 30 minutes) following removal of the cardiopulmonary bypass machine (CBM).