<正> One hundred and fifty Wistar rats were randomized into a control group with shamoperation and a left coronary artery occlusion group.Specimens of the blood and myocardiumwere collected at different intervals m 2 months after operation.The morphological changes ofthe myocardium were observed trader optical and electron microscope.Malondialdehyde（MDA）level of the serum and myocardial homogenate

and the activities of lactic dehydrogenase（LDH）

succinic dehydrogenase（SDH）and ATPase and histochemical changes of calcium in the ischemicmyocardium were studied.It was found that the mafia changes of myocardial infarction weremyocardial necrosis in the early stage and repair in the late stage.The ultrastructural changes ofischemic injury appeared quite early and involved ahnost all the subcellular organelles.The repairin the late stage was mainly incomplete regeneration of a few myoo.trdM cells.The significanceof the“junction-like”structure of fibroblasts was not dean

it was probably one of themorphological basis of scars.The activities of the enzymes were quickly suppressed afterocclusion

which suggests the exhaustion of energy metabolism.The MDA level of the myocardialhomogenate elevated in the first 24 h after occlusion

suggesting that myocardial ischemia can in-crease lipid peroxidation reduced by oxygen free radicals

It might be one of the Factors of theirreversibility of ischemic myocardial damage.