We studied the presence of colony-forming cells in cell culture from rat heart 40 days after experimental myocardial infraction. The mean cellularity in this pathology was 12+/-8 cell/cm2, which is 20-fold lower than in intact myocardium. Transplantation of mesenchymal stem cells into the remodeling myocardium restored the pool of colony-forming cells. This effect depended on the state of transplanted cells. After transplantation of mesenchymal stem cells with low content of stress proteins, 6+/-2 colonies were detected, while after transplantation of cells with high content of hsp70 and hsp60 stress proteins (modified mesenchymal stem cells) 18+/-5 colonies were found, the mean cellularity of the corresponding cultured being 946+/-267 and 1926+/-123 cell/cm2. The positive effect of modified mesenchymal stem cells was observed on days 4 and 7 after transplantation. We conclude that postinfarction remodeling mobilized the total pool of regional stem cells; mesenchymal stem cells with high content of hsp70 and hsp60 demonstrated highest survival rate after intramyocardial transplantation.