Files in this Data Supplement:

• Movie - (.mov) (12 MB). The video clip shows spontaneous beating of the grafted neonatal cardiomyocytes at 2 weeks after implantation. Examples in 2 separate rats are shown. The rats were anesthetized and placed in the supine position. The aorta was exposed through the abdominal midline incision and the transverse incision along the 12th rib. The direction of the aorta is running from top to bottom. After excision of the heart, the neonatal cardiomyocytes engrafted into the aorta (between the diaphragm and the take-off of the renal artery) showed spontaneous rhythmic beating. The only explanation for the beating in the absence of the heart is spontaneous beating of the implanted cardiac cells.