Objective To simulate and assess the clinical effect of intracoronary infusion of bone marrow mononuclear cells or peripheral endothelial progenitor cells on myocardial reperfusion injury in mini-swine model. Methods Twenty-three mini-swine with myocardial reperfusion injury were used as designed in the study protocol. About (3.54∓0.90)??108 bone marrow mononuclear cells (MNC group

n=9) or (1.16∓ 1.07)??107 endothelial progenitor cells (EPC group

n=7) was infused into the affected coronary segment of the swine. The other mini-swine were infused with phosphate buffered saline as control (n=7). Echocardio- graphy and hemodynamic studies were performed before and 4 weeks after cell infusion. Myocardium infarction size was calculated. Stem cell differentiation was analyzed under a transmission electromicroscope. Results Left ventricular ejection fraction dropped by 0% in EPC group

2% in MNC group

and 10% in the control group 4 weeks after cell infusion

respectively (P<0.05). The systolic parameters increased in MNC and EPC groups but decreased in the control group. However

the diastolic parameters demonstrated no significant change in the three groups (P>0.05). EPC decreased total infarction size more than MNC did (1.60&mnplus;0.26 cm2 vs. 3.71&mnplus;1.38 cm2

P<0.05). Undermature endothelial cells and myocytes were found under transmission electromicroscope. Conclusions Transplantation of either MNC or EPC may be beneficial to cardiac systolic function

but might not has obvious effect on diastolic function. Intracoronary infusion of EPC might be better than MNC in controlling infarction size. Both MNC and EPC may stimulate angiogenesis

inhibit fibrogenesis

and differentiate into myocardial cells.