Aim To examine the effects of mesenchymal stem cells (MSC) intramyocardial injection after infarction on extracellular collagen matrix (ECCM),angiogenesis in ischemic myocardium and left ventricular function in ischemia-reperfused rats. Methods We created infarction in rat by ligaturing coronary anterior descending branch for 60 min and reperfused,administered DAPI-labeled allogeneic bone MSC intramyocardial injection before reperfusion and measured vessel density,cross-sectional area of viable myocardium,indexes of expansion and left ventricular remodeling,collagen volume fraction,and hemodynamic parameters at 7 and 28 days post-surgery. Results The infarct size were reduced and indexes of remodeling attenuated significantly,but without apparent improvement of ventricular function at 28 days post MSC injection. DAPI was found in infarct,and peri-infarct myocardium,some of them were vWF and α-SMA positive,which suggested that MSC might differentiate into smooth muscle cells and endothelial cells,result in increasing the vessel density in periphery region of infarction and reducing collagen profile. Conclusions In a ischemia-reperfusion rat MI model,MSC myocardial transplanted differentiated into vessel smooth muscle and endothelial cells,increased vascularity and therefore reduced infarct size and ECM,but without improving cardiac function.