Scar formation and resorption during healing of myocardial infarction after cryoinjury. (A-F and H) Heart sections stained with AFOG representing the subsequent stages after cryoinjury. (A) At 4 dpci (days post cryoinjury), the damaged myocardium (dark orange) becomes surrounded by non-muscle cells (light gray, denoted by arrow). (B) At 7 dpci, a fibrin layer (red) forms along the inner side of the wound margin that consists of non-myocytes (arrow). The central part of the post-infarct consists of a loose collagen network (blue). (C) At 14 dpci, the edges of the fibrin layer (red) resolve and are replaced by new myocytes (orange arrow). The central part of the post-infarct contains abundant collagen fibers (blue). (D) At 21 dpci, a wall of cardiac tissue surrounds the entire infarct (orange arrows). Fibrin (red) is markedly reduced, while the collagen fibers (blue) persist. (E) At 30 dpci, no fibrin is visible. The collagen-containing area has markedly decreased. (F) At 60 dpci, the infarct scar is nearly completely resolved. Only occasionally, a few collagen fibers are detected (blue arrow). (G) A change of the scar size relative to the entire ventricle at different stages after injury. For measurements, all cross sections of six hearts per time point were analyzed. (H) In control, at 4 dps (days post sham), no fibrin or collagen fibers are present. Scale bar in (A), 300 μm.