Two groups of patients were prospectively studied to evaluate the hemostatic effects of high-dose aprotinin in open heart operations. Group A patients (n = 22) received aprotinin during the entire surgical procedure. Group B patients (n = 12) served as controls. The groups were homogeneous for base variables and for cardiopulmonary bypass duration. Postoperative bleeding was lower in group A (mean, 486 mL) than in group B (830 mL) (p less than 0.01). The need for banked blood decreased by approximately half in the aprotinin patients (mean: group A, 213 mL; group B, 409 mL). Hemoglobin levels were similar in the two groups (postoperative day 7: group A, 11.29 g/100 mL; group B, 11.26 g/100 mL; NS). Platelet count decreased at the end of operation in both groups (99,000 and 95,000/mL, respectively; NS) and then increased beyond baseline levels before discharge. No complications were observed that could be attributed to aprotinin. In conclusion, we believe that the use of high-dose aprotinin is safe and effective. It decreases blood loss and reduces the need for banked blood in cardiac operations, particularly in select groups of patients (eg, those undergoing reoperation, Jehovah's Witnesses, those with renal failure).