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Figure 4 Skeletal fast and slow twitch myosin. Shown are surviving skeletal myofibers in the heart from Patient 5 stained with trichrome (A and B), skeletal-specific fast myosin MY-32 (identification of fast twitch skeletal muscle myosin isoforms only) (C) and myosin heavy chain beta slow (D). A, C, and D show adjacent sections from the same graft site, and B shows a different graft site from the same patient, but where the myofibers can be seen in a longitudinal profile. Grafted skeletal myofibers have a distinct stain by trichrome that are marked by stars in B, and the alignment between grafted myofibers and host myofibers is striking. The area of the graft is marked by the dotted line in A, C, and D and individual skeletal myofibers that stained with slow myosin and not fast myosin (MY-32, C) are marked by arrowheads. All images were shot at the same magnification.