A heart attack patient's ECG evolves over hours; enzymes leak. The blocked coronary starves myocytes — reversible injury (swelling) for ~20 minutes, then irreversible: coagulative necrosis (proteins denature but architecture preserved — the classic infarct). Reperfusion (angioplasty) saves the border zone but free radicals injure some rescued cells — reperfusion injury. Days later macrophages clear the dead, weeks later a fibrous scar remains — the heart can't regenerate muscle, only scar. Every infarct is this timeline.