Cardiac surgery and cardiopulmonary bypass produces bleeding and the need for allogenic blood product transfusions in many patients. Blood conservation is important in the perioperative management of patients. Aprotinin, a serine protease inhibitor isolated from bovine lung, is a complex protease inhibitor that is an antifibrinolytic, inhibits contact activation, and decreases the inflammatory response to cardiopulmonary bypass. Aprotinin reduces blood loss and transfusion requirements in adult and pediatric patients undergoing cardiac surgery with cardiopulmonary bypass. Full-dose aprotinin significantly reduces postoperative blood loss and has been demonstrated in multiple prospective blinded studies to be safe and effective. One of the major adverse effects is anaphylaxis that occurs on re-exposure to aprotinin.