Stem cells have become one of the predominant topics in biology and medicine. Stem cells are the precursor cells of every tissue in the body, and thus have the potential to provide replacement tissue for diseased and damaged organs. Because of the inherent capacity of stem cells to produce a multitude of different tissues, these cells promise great advances in the treatment of many medical conditions. To date, this promise is just that: a promise. However, the stem cell field is still in its infancy and is now garnishing great interest among researchers. Thus, the next several years will undoubtedly provide great progress in understanding these cells, and with it the knowledge to manipulate their behavior for medical therapy. Research in the stem cell field will undoubtedly have great impact on treatment of the cardiovascular system. Cardiac disease is the number one cause of mortality and morbidity among the United States population. Since stem cells offer a potential therapeutic alternative to organ and tissue transplantation, advances in stem cell biology will significantly increase the future medical options for treating cardiovascular diseases.

To understand both the current state and future potential of stem cell biology and medicine, the articles in this special issue address a number of important questions. What are the characteristics of stem cells? What are the developmental origins of the stem cells that give rise to the various cell phenotypes that comprise the fully developed heart? Do the initial aggregate of nondifferentiated cells that arises following fertilization—the embryonic stem (ES) cells—possess unique capabilities as a source of replacement cardiovascular tissue? How do stem cells that are present in the adult differ from those within the developing embryo? How broad is the potential of tissue-derived stem cells to generate various types of differentiated tissue? What are the regulatory mechanisms by which cardiovascular stem cells are induced to undergo cell differentiation, and how can this information be applied to manipulating stem cells for medical therapies? What is the long-term prognosis for using stem cells to combat cardiovascular disease? Although stem cell biology has not progressed to the point where any of these questions can be answered definitively, we believe that the articles within this issue will provide both a summation of our current understanding of cardiovascular stem cells and a road map to future research directions in this field.