BACKGROUND: Aprotinin is a potent, nonspecific broad serine protease inhibitor. It's inhibitory effects on intrinsic pathway of coagulation cascade can augment anticoagulation by heparin. This study designed to demonstrate augmented anticoagulation of aprotinin to heparin contaminated blood on thromboelastography(TEG). METHODS: This study designed into two phases for 21 healthy volunteers undergoing elective opeation. The first phase study, it was for looking at TEG differences between blood treated with aprotinin 200 KIU and blood treated with heparin 0.05 unit and 0.1 unit per blood 1 ml. The second phase study was for looking at anticoagulation of aprotinin added by heparin 0.05 unit and 0.1 unit per blood 1 ml and their reversal added by optimal dose of protamine sulfate. RESULTS: The aprotinin treated blood showed only a prolonged reaction time. Blood treated with incremental dose of heparin showed longer reaction time and smaller alpha angle than TEGs of native blood. Aprotinin added to the heparin contaminated blood showed much longer reaction time and much less alpha angle when compared with TEGs of aprotinin or heparin treated blood. Depressed TEG pattern by the heparin and aprotinin mixture reversed back to the TEGs of blood treated with aprotinin when optimal dose of protamine added. CONCLUSIONS: Those results suggest that aprotinin administered in open cardiac surgery can augment the remained anticoagulation effect due to heparin even after first dose fo protamine after weaning of cardiopulmonary bypass. This is of clinically improtance to distinguish heparin related coagulopathy from heparin non related coagulopathy by thromboelastography.