OBJECTIVE To determine the safety and effectiveness of autotransfusion of shed mediastinal blood after open heart surgery. METHODS Sixty patients undergoing coronary artery bypass grafting (CABG) were selected randomly to receive either nonwashed shed mediastinal blood (Group 1, n = 30) or banked blood (Group 2, n = 30). Drainage and transfusion volume were determined after the operation. Hb, RBC, HCT and PLT were detected immediately before and after the operation, as well as 24 hours and 7 days after the operation. Data were analyzed using Fisher's exact test. A P < 0.05 was considered significant. RESULTS There were no significant differences in Hb, HCT, PLT or length of cardiopulmonary bypass (CPB) (P > 0.05). In the two groups, no significant difference in the mean blood loss was observed during 24 hours after the operation (660 +/- 300 ml in Group 1 and 655 +/- 280 ml in Group 2, P > 0.05). In Group 1, the mean volume autotransfused was 280 +/- 160 ml, and the patients required 360 +/- 80 ml banked blood compared with 660 +/- 120 ml in Group 2. In other words, the banked blood requirement in Group 1 was 40% lower. CONCLUSIONS Autotransfusion of shed mediastinal blood after an open heart operation is safe and effective.