The accepted paradigm considers the adult mammalian heart as a postmitotic organ, which possesses a relatively constant number of myocytes from shortly after birth to adulthood and senescence. This notion is questioned by the demonstration that although most adult myocytes are terminally differentiated, there is a small and continuously renewed subpopulation of cycling myocytes produced by the differentiation of cardiac stem-like cells. Myocyte death and myocyte regeneration are introduced as major determinants of cardiac homeostasis and alterations of ventricular anatomy and function in physiological and pathological states. The possibility of reconstituting dead myocardium by stem-like cells is advanced and proposed as a major area of future research.