In comparison, the distended LV model using a 2-week-old donor. (a) A photograph of a transplanted donor heart in situ. (b) Representative echo images showing the apical long axis view of the LV. An AR jet was detected in a 2D echocardiography with color Doppler. (Ao: aorta). (c) Representative Hematoxylin and Eosin- and Masson’s Trichrome-stained slides sectioned along the short axis. Collagen-rich fibrous layers (stained in blue) are seen in the subendocardial layer of a 2-week-old donor heart. (d) A Masson’s Trichrome-stained slide from a neonatal donor heart for comparison. Fibrous layers are located on the endocardial surface of the LV. Black scale bar, 1 mm; white scale bar, 200 μm.