AIM:Toobservetheeffectsofmicroparticlesderivedfrombonemarrowmesenchymalstemcells ( MSC-MPs) on angiogenesis and cardiac function in a rat myocardial infarction model .METHODS:MSCs were obtained from Sprague-Dawley rats.MSCs were treated under serum-free condition in hypoxia for 72 h, and the microparticles were isolated from the supernatants .The phenotypic profile of MSC-MPs was determined by bead-based flow cytometry and the morphology was observed under a transmission electron microscope .The rat myocardial infarction model was established . The cardiac function was evaluated by echocardiography after the intramyocardial injection of MSC -MPs.The myocardial in-farct size was observed by Masson staining .The blood vessel density in the peri-infarcted area was measured using immuno-histochemical staining for von Willebrand factor and α-smooth muscle actin.The expression of vascular endothelial growth factor ( VEGF) was analyzed by real-time PCR.RESULTS: Apoptotic MSCs released a large quantity of microparticles which were phenotypically similar to the parent MSCs and 100~1 000 nm in diameter.The cardiac functions of myocardial infarction rat model were improved at 7 d and 28 d after intramyocardial injection of MSC-MPs compared with control group . The myocardial infarct size was reduced and angiogenesis was promoted significantly in the infarcted heart injected with MSC-MPs 28 d after treatment .MSC-MPs treatment also increased the expression level of VEGF within 7 d.CONCLU-SION:MSC-MPs protect cardiac tissue from ischemic injury and improve cardiac function by promoting angiogenesis after myocardial infarction .