Abstract: AIM：To investigate the effects of bone-marrow-derived endothelial progenitor cell (EPC) transplantation on left ventricular (LV) remodeling after myocardial infarction in swine and its potential mechanism. METHODS: The left anterior descending coronary arteries of swine were obstructed by balloon to create myocardial infarction models. Two weeks later, EPCs were collected from bone marrow of the swine by density gradient centrifugation, cultured and amplified in vitro for 1 week. EPCs or medium was then injected into the infarction-related coronary arteries through balloon catheter. After 4 weeks, cardiac function was measured by echocardiography and ventriculography, and the apoptosis rates were assessed by flow cytometry. RESULTS: At 4 weeks after transplantation, LV end-diastolic dimension decreased in the transplantation group (P<0.01) but increased in the control group. Left ventricular function was improved greatly in the transplantation group (P<0.01) but no obvious changes were observed in the control group. The apoptosis rates in the border infarct regions decreased in the transplantation group compared with those in the control group (P<0.05). CONCLUSION: EPC transplantation attenuates the degree of post-MI LV dilation and the development of infarction area and reduces the apoptosis rates of myocardium in the border infarction regions, which may be responsible for the improvement of ventricular remodeling following myocardial infarction.