Role of cardiac stem cells in cardiac pathophysiology: a paradigm shift in human myocardial biology.

For nearly a century, the human heart has been viewed as a terminally differentiated postmitotic organ in which the number of cardiomyocytes is established at birth, and these cells persist throughout the lifespan of the organ and organism. However, the discovery that cardiac stem cells live in the heart and differentiate into the various cardiac cell lineages has changed profoundly our understanding of myocardial biology. Cardiac stem cells regulate myocyte turnover and condition myocardial recovery after injury. This novel information imposes a reconsideration of the mechanisms involved in myocardial aging and the progression of cardiac hypertrophy to heart failure. Similarly, the processes implicated in the adaptation of the infarcted heart have to be dissected in terms of the critical role that cardiac stem cells and myocyte regeneration play in the restoration of myocardial mass and ventricular function. Several categories of cardiac progenitors have been described but, thus far, the c-kit-positive cell is the only class of resident cells with the biological and functional properties of tissue specific adult stem cells.