Heart disease, congenital and acquired, is a major factor contributing to human morbidity and mortality and arises from a range of abnormal cardiac and vascular defects. Cell therapy is widely viewed as being a viable strategy that can be used to regenerate and repair the cardiovascular system but it is still not clear which source of cells will be best suited to this task. Many of the uncertainties relating to the use of cell therapy in cardiovascular repair arise from our relatively poor understanding of stem cell populations in the heart and the potential of noncardiac cells to participate in heart regeneration. This situation is swiftly changing, however, with recent discoveries showing that multipotent stem cells in the heart can regenerate cardiac tissue and that similar cell types can be generated from embryonic stem cells in vitro.