Embryonic stem cells are pluripotent cells derived from blastocyst-stage embryos. They are characterized by their capacity for self-renewal and by the ability to differentiate into a variety of cell types. In vitro, ES cells can spontaneously aggregate into the formation of embryoid bodies (EBs) comprised of a range of differentiated cells. When injected into severe combined immunodeficient (SCID) mice, ES cells will induce the generation of teratomas, which include differentiated cells from three embryonic germ layers. We can induce the differentiation of ES cells into cardiocytes by treatment with several growth factors or co-culture with certain other cells. The pure differentiated cardiocytes from ES cells are then selected and implanted into the infarcted hearts. The hearts' function will be improved. ES cells implantation is a novel and potential method to treat infarcted hearts.