Residual heparin effects after protamine reversal is a potential bleeding disorder associated with cardiopulmonary bypass(CPB). To differentiate this from the other multiple factors causing coagulopathy should be initialized in the setting of management. The purpose of this study was to compare simple activated clotting time(ACT) and thromboelastography(TEG) with heparinase treated ACT and TEG for detecting residual heparin effects to distinguish rapidly the presence of heparin from the effects of other factors because the enzyme heparinase specifically neutralized heparin. After institution approval, 20 patients who required open heart surgery were studied. Baseline kaoline ACT, heparinase ACT, TEG and heparinase TEG(Haemoscope) were obtained before CPB on the same blood sample. The repeated tests were performed on the same blood samples 20 minutes after protamine reversal following CPB. Differences between heparinase treated tests and untreated tests were also evaluated at the same time. Wilcoxon signed ranked test was used to compare the results between before and after bypass. None of patients had significant postoperative bleeding complication. All tests before bypass were normal. Twenty minutes after protamine reversal, 3 patients showed kaoline ACT were extended above 10% of the value of heparinase ACT but all of them remained within normal range. However, nearly all patients showed heparin effects on TEG. The heparin effects on TEG were defined as significant differences in all of parameters, especially in alpha angle and R+K time between simple TEG and heparinase TEG. In Conclusion, heparinase treated ACT and native ACT are not sensitive to residual heparin effects after CPB. Their normal results did not preclude residual heparin effects on heparinase modified TEG. However, it might be further investigated to need additional protamine in the case of residual heparin effects on TEG.