Abstract： Objective To investigate the effect of Shenfu injection (SFI) on hypoxia and reoxygenation (H/R)-induced apoptosis and the expression of Bcl-2 and Caspase-3 in cultured neonatal rat cardiomyocytes and to explore the possible molecular protective mechanisms of SFI from hypoxia and reoxygenation injury in cardiacmy-ocytes in vitro. Method The experiment was performed in Research Center for Cardiovascular Regenerative Medicine, Cardiovascular Institute and Fuwai Hospital in Beijing. Ventricular myocytes from the hearts of neonatal Sprague-Dawley rats (1- to 2-day old) were cultured. The model of hypoxia and reoxygenation injury was devel-oped in primary cultured neonatal rat cardiacmyocytes. The cultured cells were randomly divided into four groups: (1) Control group (Con group), without any treatment; (2) Hypoxia and Reoxygenation group (H/R group),4 h hypoxia followed by 16 h reoxygenation; (3) Low-dose SFI group (L-SFI group),cardiacmyocytes were pretreated with a low dose (50 μL/mL) of SFI for 30 min followed by H/R; (4) High-dose SFI group (H-SFI group),car-diacmyocytes were pretreated with a high dose (100 μL/mL) of SFI for 30 min followed by H/R. Apoptosis was quantified by fluoreacence-activated cell sorter (FACS) analysis after staining with Fluorescein isothiocyanate (FITC)-labled Annexin-V (Annexin V-FITC) and propidine iodide (PI). The expressions of Bcl-2 and Caspase-3 were detected by ECL-Western blot analysis. All data are expressed as mean±S.E.M. One-way analysis of vari-ance (ANOVA) was performed followed by Student-Newman-Keul test using SSPS 11.5 software. A p value less than 0.05 were considered as statistically significant. Results The results of FACS analysis indicated that the rate of different apoptotic process in cardiomyocytes was significantly increased after H/R, while after SFI treatment the occurrence of cell apoptosis induced by H/R was decreased significantly. The results of ECL-Western blot analysis showed that cells' exposure to H/R induced proteolytic cleavage of caspases,as revealed by the appearance of the characteristic fragment at 17 000 of Caspase-3 and this proteolytic activation was nearly completed with difference concentration SFI incubation. The anti-apoptotic protein Bcl-2 in cardiomyocytes was decreased after H/R insult and was increased in cells with SFI pretreatment. Conclusions SFI has protective effects on cardiacmyocytes a-gainst apoptosis that could be induced by H/R injury, the mechanisms of which probably involve the inhibition of down-regulation of Bcl-2 protein level and sequential activation of Caspase-3.