Legend. Transplantation of undifferentiated human embryonic stem cells (hESC) in rat infarct resulted in teratoma-like formations (A). Grafted ex vivo differentiated cardiomyocyte derivatives (hESC-CM) matured, proliferated, aligned, and formed gap junctions with host tissue (B), which attenuated remodeling and improved LV function. See pages 1887 and 1888.