Abstract: AIM To investigate the myocardial protective effect of danhong injection in chronic stress reaction of rats by observing myocardial enzyme and expression of heat shock protein 70 (HSP70). METHODS Fifty-five healthy adult Sprague Dawley rats were randomly divided into blank control group, danhong injection control group, chronic stress group, and chronic stress danhong injection group. The blank control group was treated with neither chronic stress nor danhong injection. The danhong injection control group was treated with intraperitoneal injection of danhong (daily 10 ml/kg) but not the chronic stress group. The chronic stress group was treated according to the chronic stress model processing and the chronic stress danhong injection group was treated in accordance with the treatment of chronic stress reaction model and intraperitoneal injection of danhong injection (daily, 10 ml/kg). After 3-week chronic stress, rats in the four groups were killed, changes of myocardial enzyme were observed, and expression of HSP70 in myocardial tissue was detected using immunohistochemical method. RESULTS Compared with those in the blank control group, lactate dehydrogenase (LDH) and creatine kinase isoenzyme (CK-MB) in the danhong injection control group, chronic stress group, and chronic stress danhong injection group significantly increased (P<0.01). LDH and CK-MB in the chronic stress group increased significantly compared with those in the danhong injection control group (P<0.05) and LDH and CK-MB in the chronic stress danhong injection group decreased significantly compared with those in the chronic stress group (P<0.05). But no significant difference was found between the danhong injection control group and the chronic stress danhong injection group. Expression of HSP70 of myocardial tissue in the danhong injection control group, chronic stress group, and the chronic stress danhong injection group were stronger than that in the blank control group. There was no significant difference between the danhong injection control group and the chronic stress group. However, the expression of HSP70 in the chronic stress danhong injection group was stronger than that in the danhong injection control group and the chronic stress group. CONCLUSION Danhong injection effectively inhibited the increase of LDH and CK-MB in chronic stress rats and increased the expression of HSP70 in myocardial tissue of chronic stress rats.