BACKGROUND: The protease inhibitor aprotinin reduces blood loss and homologous blood usage after a cardiac operation. The aim of the present study was to investigate the effect of low- and high-dose aprotinin on thromboelastography (TEG) variables and to examine the relationship between the clinical effect of aprotinin and the TEG variables in coronary artery bypass grafting surgery (CABG). METHODS: Twenty-three patients scheduled for an elective CABG were randomly assigned to receive either high does (group H, n = 12) or low does (group L, n = 11) aprotinin. TEG variables, and a coagulation profile test at baseline and arrival in ICU were performed. Amount of blood loss, homologous blood transfusion and heparin requirements were measured. RESULTS: In group L, there were significant increases in r time and k time and significant decreases in MA and alpha angle after aprotinin administration. In group H, just k time after aprotinin administration was significantly increased compared with baseline data. There were no significant differences in amount of blood loss and allogenic blood transfusions between the two groups. There was not a significant correlation between TEG variables and amount of blood loss in both groups. Interestingly a siginificant negative correlation between the length of cardiopulmonary bypass and MA was noted in group H (r = -0.63; P < 0.05). CONCLUSIONS: In CABG patients, aprotinin preserves platelet function more significantly in the high-dose aprotinin group. In addition, TEG variables indicated a later clot formation in the low dose aprotinin group.