Postmortem, heart and lung weights were measured and hematoxylin-eosin–stained heart, lung, liver, and spleen tissue were surveyed. Cardiac interstitial fibrosis was quantified by computerized imaging analysis (cellSens 1.3; Olympus, Tokyo, Japan) of phosphotungstic acid hematoxylin-stained sections. Myocardial disarray was evaluated by laser confocal microscopy (Zeiss LSM 510; Carl Zeiss, Thornwood, NY) following sarcomeric α-actinin (1:200; Sigma-Aldrich, St Louis, MO), along with nuclear 4′,6′-diamidino-2-phenylindole (Molecular Probes, Eugene, OR) staining. Cell proliferation and cardiac stem cells were evaluated by immunostaining for Ki67 (1:400; D3B5; Cell Signaling Technology, Danvers, MA) and Sca-1 (1:100; R&D Systems, Minneapolis, MN), respectively.26 (link) Engraftment of implanted iPS cells was tracked using a β-galactosidase antibody (1:5000; Abcam, Cambridge, MA). Ultrastructural evaluation, including percent area of myofibrils in cytoplasm,27 (link),28 (link) was performed by transmission electron microscopy (JEOL 1200 EXII; JEOL Ltd, Tokyo, Japan).