We describe here the identification of a subpopulation of primitive cells from rat heart, processing stem cell marker, c-kit and myogenic transcriptional factors, GATA-4 and MEF 2C, and cardiac specific proteins, troponin-I, alpha-sarcomeric actinin and connexin-43. They exhibited a high in vitro proliferative potential. These findings strongly suggest that these cells are putative cardiomyocyte precursors. After transplantation, they were able to be retained and proliferate (13.63 +/- 5.97% after 2 weeks) within the ischemic heart. Progeny of implanted cells migrated along the infarcted scar, reconstituted regenerated cardiomyocytes with incorporation into host myocardium, and inhibited cardiac remodeling with decreased scar formation.