Abstract: AIM To investigate hemotaxis of 5-aza-2’-deoxycytidine (5-aza-CdR) induced MSCs to damaged myocardium of infarction-induced heart failure in rats through tail vein transplantation and to study the distribution characteristics and the transplantation effect on rattus α-MHC mRNA expression in infarction region. METHODS Wistar rat MSCs were cultured in vitro and the second passage MSCs were incubated together with 5-aza-CdR (0.3 μmol/L) for two times. The induced MSCs labeled with bromodeoxyuridine (BrdU) were then transplanted through tail vein into the rats of infarction-induced heart failure at different time point (1 d, 8 d, 3 w and 1 m after myocardial infarction). Three days and 1 month after transplantation, the homing ability of MSCs to the damaged myocardium and the distribution characteristics were studied by immunohistochemistry. α-MHC mRNA expression in the infarction region was also detected 1 month after transplantation by RT-PCR. RESULTS Three days after MSCs transplantation at different time periods, anti-BrdU positive cells were found in all groups. The donor MSCs were mainly in the damaged myocardium. In acute or subacute period, many donor MSCs were well mixed with the cells. In chronic period, donor MSCs decreased in number and aligned with fibers. One month after transplantation, anti-BrdU positive donor cells could still be seen in some rats. The distributing characteristics were similar to those 3 days after transplantation. No significant difference of rattus α-MHC mRNA expression was found in infarction region between MSCs transplantation 1 d or 8 d after infarction and MSCs transplantation 3 w after infarction. The rattus α-MHC mRNA expression in infarction region in MSCs transplantation 3 w after infarction improved and was significantly different compared with that in DMEM transplantation group (P<0.01). But there was no significant difference between the MSCs transplantation group and DMEM transplantation group when transplanted 1 month after infarction. CONCLUSION MSCs transplanted through tail vein at different time point after myocardial infarction mainly home to the infraction region and the distribution characteristics are related to myocardial pathology at the time of transplantation. The earlier MSCs are transplanted after myocardial infarction, the higher is the rattus α-MHC mRNA expression in infarction region.