Appearances of myocardial infarct after 12-24 hours. Myocardial infarction or a heart attack occurs when blood flow to part of the heart is obstructed. This restricts the oxygen to the heart and causes tissue death. Histologically, the infarcted muscle is brightly eosinophilic (stained with eosin) with intercellular edema (swelling caused by excess fluid). (See 2Y0199, 2Y0200 and 2Y0426)