Cardiomyocyte regeneration may occur during physiological and pathological states in the adult heart; these data highlight the possibility that myocardial regeneration may occur via cardiomyocyte proliferation and/or differentiation of putative cardiac stem cells. To date, various cell types have been used for cardiac repair, including skeletal myoblasts, bone marrow-derived cells, mesenchymal stem cells, endothelial progenitor cells, umbilical cord blood stem cells, cardiac stem cells, and embryonic stem cells. This chapter will review each of these different stem cell populations in regard to the potential treatment of heart disease. It begins by examining the in vitro and in vivo animal studies, and then briefly discusses the cell therapy clinical trials that are currently underway for treating ischemic heart disease. © 2009 Humana Press.