This high power microscopic view of the myocardium shows an infarction of about 1 to 2 days in duration. The myocardial fibers have dark red contraction bands extending across them. The myocardial cell nuclei have almost all disappeared. There is beginning acute inflammation. Clinically, such an acute myocardial infarction is marked by changes in the electrocardiogram and by a rise in the troponin I and the MB fraction of creatine kinase in the serum.

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