Abstract: AIM To experimentally investigate the effect of direct intramyocardial administration of 17β-estradiol loaded nanoparticles on myocardial angiogenesis in rats after myocardial infarction. METHODS 17β-estradiol loaded nanoparticles were prepared by a solvent evaporation method. Release parameters were detected in vitro experiment. Myocardial infarction was induced by left coronary artery ligation in ovariectomized female rats treated with intramyocardial administration of 17β-estradiol loaded nanoparticles (4 mg/100 g). One month later, the microvascular density (MVD) and eNOS protein expression in myocardium of the rats were analyzed by immunohistochemistry and the serum levels of 17βestradiol were measured by RIA method. RESULTSIn vitro 17βestradiol release was maintained at a constant rate from these PLGA nanoparticles for 1 month. One month after operation, the MVD and eNOS protein expressions were higher in myocardium of rats in ET group than those in MI group (P<0.05). A significant decrease in MVD and eNOS protein expression was observed in OMI grou, compared with that in MI group. CONCLUSIONS 17β-estrogen deficiency induced by oophorectomy negatively affects myocardial angiogenesis. Local intramyocardial administration of 17βestradiol loaded nanoparticles can effectively promote angiogenesis of myocardium in rats, which may attribute to the increased eNOS protein.