Abstract: To further demonstrate reperfusion injury to post-ischemic canine myocardium, the present experiments were performed to investigate the effecof myocardial ischemia on activity and localization of succinic dehydrogenase(SDH) in the groups of occluding left anterior descending coronary artery for 60 and 90 min. followed by reopening for 120 min. by enzyme histochemistry and cytochemistry. SDH activity decreased in the group of coron ary occlusion for 60 min., especially for 90 min. Reperfusion for 120 min. resulted in much decrease of SDH activity and chaotically extended distribution. In conclusion, reperfusion causes much more severe injury to the postischemic canine myocardium, i.e, reperfusion injury, which may be, considered as one of the leading causes of cardiac death in forensic pathology.