Objective To investigate the protective effect and mechanism of activated protein C ( APC) on myocardial ischemia reperfusion injury in rats. Methods Thirty male SD rats were randomly divided into sham operation group (10), I/ R group (10) and apc-treated group (10). The anterior descending branch of the left coronary artery was ligated for 60 min, and the myocardial ischemia reperfusion model was established 6 h after reperfusion. The expression levels of TNF-α, MPO and ICM-1 were detected by ELISA and immunohistochemistry. HE staining was used to detect the changes of myocardial pathology in each group.Results Compared with the sham group, the expression of TNF-α, MPO and ICAM-1 were increased significantly in the I/ R group (P< 0. 01); but compared with the I/ R group, the expression of TNF-α, MPO and ICAM-1 were obviously decreased in the APC group (P< 0. 01). Conclusions APC has a protective effect on myocardial I/ R injury, in a mechanism that may involve inhibiting the expression of inflammatory factors and reducing the infiltration of inflammatory cells.