Based on Harvard criteria findings, comparative morphological investigation on postmortem heart muscle biopsy following coronary insufficiency after sudden cardiac death have been reported. The subendo-thelial layer of the left ventricular wall has revealed a severe interstitial edema, various types of actin-myosin filamental destruction, mitochondrial damage, and disseminated muscle fiber necrosis. One of the first alterations observed was the change in transmembrane calcium and intracellular calcium metabolism. A decrease in succinic dehydrogenase and cytochrome oxidase activity was discovered early.