Cell apoptosis during the replacement of the scar with a new myocardium. (A-C) Confocal images of quadruple-stained cross-sections of hearts at different time points after cryoinjury. Cardiomyocytes are labeled by the presence of TPM (blue) and MEF-2 (red). All the nuclei are visualized by DAPI (yellow) and the apoptotic cells are detected by the TUNEL assay (green). Dashed lines encircle the scar. (A', B' and C') Higher magnifications of framed area shown in left panels. (A-A') At 4 dpci, a large infarct area is devoid of cardiomyocytes, and it contains abundant apoptotic cells. (B-B') At 14 dpci, numerous non-myocytes located in the infarct zone undergo apoptosis. Arrows indicate new myocardium invading the post-infarct. (C-C') At 30 dpci, cell apoptosis is no longer detected in the remaining post-infarct region. Cardiomyocytes have replaced a large portion of the wound, and only a small area lacks cardiomyocytes. Arrowheads denote a new myocardial wall. Scale bars in (A-A') represent 300 μm.