Time after myocardial infarction

Predominant light microscopic changes

0-4 hours

• No visible change

4-12 hours

• Wavy fibers with narrow, elongated myocytes

12-24 hours

• Myocyte hypereosinophilia with pyknotic (shrunken) nuclei

1-3 days

• Coagulation necrosis (loss of nuclei & striations)
• Prominent neutrophilic infiltrate

3-7 days

• Disintegration of dead neutrophils & myofibers
• Macrophage infiltration at border areas

7-10 days

• Robust phagocytosis of dead cells by macrophages
• Beginning formation of granulation tissue at margins

10-14 days

• Well-developed granulation tissue with neovascularization

2-8 weeks

• Progressive collagen deposition & scar formation