The prospect of improved regeneration or replacement of damaged tissues and organs is the main goal of stem cell research. Embryonic stem cells have been the focus of intense study in the past 2 decades, but the biology of the adult stem cells that persevere in mature tissues has been poorly understood. The presumption that adult tissues, such as the central nervous system, have low or no self-renewal potential has been challenged by the observation that these tissues host small groups of resident stem cells that may proliferate and repopulate injured areas. In the September 19 Cell, Antonio Beltrami and colleagues at the New York Medical College report that heart also contains adult stem cells, identifying rat myocytes having the properties of cardiac stem cells (Cell, 114:763-776, September 19, 2003).