Damage to the MYOCARDIUM resulting from reperfusion of ischemic areas of the HEART. Reperfusion takes place when there is spontaneous thrombolysis, THROMBOLYTIC THERAPY, collateral flow from other coronary vascular beds, or reversal of vasospasm. Reperfusion can cause EDEMA, injuries to cardiac myocytes (MYOCYTES, CARDIAC) and the conducting tissue with resultant ARRHYTHMIA. Degree of injury depends on the duration and extent of MYOCARDIAL ISCHEMIA before reperfusion, cytosolic calcium overload, and oxygen FREE RADICALS.