Stem cell transplantation has been proposed as a novel experimental strategy to treat heart diseases, such as acute myocardial infarction and heart failure. The beneficial effects of transplanted cells may include active contribution to contractile function, passive improvement of cardiac mechanics, induction of neoangiogenesis or other indirect influences on the biology of the heart. Several cell types have been used for cardiac transplantation. These include embryonic stem cells, bone marrow stem cells, and skeletal myoblasts. Encouraging results have been obtained in experimental ischemic and non-ischemic heart disease that show sustained cell survival after transplantation, integration into the host myocardium, and functional improvement of diseased hearts. Furthermore, preliminary data, obtained in patients with acute myocardial infarction, suggest that the observation obtained in the experimental animal may be transferred to the clinical arena in the near future. These observations fueled an exciting period of discovery and high expectations followed by controversies that need to be addressed before this strategy can be added to the therapeutic options for patients with heart disease.