Objective: To investigate a single institution's changing use of aprotinin and subsequent effects on intraoperative blood product utilization (red blood cells/fresh frozen plasma) and postoperative clinical bleeding requiring reoperation. Design: Retrospective study. Setting: Single university institution (University of Chicago). Measurements: Data from 499 adult patients undergoing cardiac surgery requiring cardiopulmonary bypass (CPB) over a two-year period (February 2005 - January 2007) were reviewed. The first 12 months (Feb 2005 - Jan 2006, Group 2005-2006) of data were compared with that from the second 12-month period (Feb 2006 - Jan 2007, Group 2006-2007). Information regarding patient demographics, surgical procedures, aprotinin use (none, half-dose, full-dose), and blood product use during CPB was retrospectively retrieved and analyzed. Main Results: When Group 2006-2007 data was compared with that from Group 2005-2006, full-dose aprotinin use had significantly decreased (58% to 17%, P < 0.001), non-use of aprotinin significantly increased (18% to 47%, P < 0.001), while fresh frozen plasma (FFP) utilization during CPB significantly increased (24% to 36%, P = 0.004). Red blood cell (RBC) transfusion rates remained stable (67% - 69%) yet rates of RBC and FFP transfusion during CPB significantly increased (23% to 34%, P = 0.003). There was also a trend toward increased unplanned reoperations for excessive clinical bleeding (0 pts in Group 2005-2006, three pts in Group 2006-2007). Conclusions: As the institution's use of high-dose aprotinin has significantly decreased, the number of patients requiring FFP and FFP/RBC combinations during CPB has significantly increased. Furthermore, a trend toward increasing incidence of unplanned reoperations for excessive clinical bleeding was noted. (C) 2009 Elsevier Inc. All rights reserved.