A variety of adult stem cells have been used to transplant into the infarcted (MI) heart, however, comparative studies are lacking to show more suitable source of cells for transplantation. We have identified a single non-hematopoietic mesenchymal stem cell subpopulation (snMSCs) isolated from human bone marrow and clonally purified, that over 99% of them expressed MSC marker proteins and cardiomyocyte marker proteins when induction in vitro. We also compared the effects of the snMSCs with unpurified MSC (uMSCs), mononuclear cells (BMMNCs), or peripheral blood mononuclear cells (PBMNCs) on myocardial repair after induction of MI in rats. Ninety days later, we observed a better cardiac function assessed by ejection fraction, fraction of shortening and lung wet/dry weight ratios, less remodeling of left ventricle (LV), lower collagen density in the LV, and more vessels in the ischemic wall in the snMSCs transplantation group than in other cell-transplanted groups. Furthermore, the transplanted cells expressing cardiomyocyte specific proteins or vascular endothelial cell marker proteins were more in the snMSCs group than in other ones. We conclude that transplantation with single clonally purified MSCs seems to be more beneficial to the cardiac repair than with other stem cells after MI. J. Cell. Biochem. 99: 1132–1147, 2006. © 2006 Wiley-Liss, Inc.