Cardiopulmonary bypass (CPB) increases risk of postoperative bleeding and need for transfusion. The aim of this study was to evaluate the effects of aprotinin, epsilon aminocaproic acid and tranexamic acid on coagulation patterns and need for banked blood transfusion. Ninety-six consecutive patients who underwent coronary artery bypass surgery were randomly assigned to 4 groups (24 patients each). The following parameters were monitored before, during and after CPB: activated lotting time, hemoglobin, prothrombin time, activated prothromboplastin time, fibrinogen, antithrombin III, xDP, Factor VIII, Thrombin-Antithrombin Complex and plasminogen. Analysis of postoperative bleeding and need for transfusion showed that the aprotinin group had significantly lower mediastinal bleeding. Transfused patients were 2, 4, 12 and 18 respectively in the aprotinin, epsilon aminocaproic acid, tranexamic acid and placebo treated group. In conclusion the use of protease inhibitors significantly reduces postoperative bleeding and transfusion. The aprotinin-treated group had the lower need for transfusion.