Does the human heart regenerate?
Until recently, the heart of mammalians was supposed to be terminally differentiated, incapable of any cellular regeneration for replacement or repair. In the past year, several researchers7 11 have demonstrated that bone marrow stem cells will migrate to an infarction in a rat heart and regenerate myocardium. Moreover, Beltrami et al.7 have proposed that the human heart regenerates cardiomyocytes following injury. The researchers autopsied the hearts of 13 patients who had died within 2 weeks of an extensive myocardial infarction, and the hearts of 10 control subjects who have died of unrelated causes. They quantified cardiomyocyte regeneration in the free wall as the percent of cardiomyocytes engaged in cell cycling. For a more stringent result, they also identified the number of cardiomyocytes that were in the final stage of the cell cycle, namely mitosis, and calculated the mitotic index the ratio of cells in mitosis to cells not undergoing mitosis. In the infarct hearts, in the ar
