Left descending coronary ligation was performed on 70 dogs and divided into four groups. I. group - permanent occlusion (5 dogs 60 min, 5 dogs 120 min, 5 dogs 180 min), II. group - 15 dogs (60 min occlusion + 120 min reperfusion), III. group - 20 dogs (60 min occlusion, 15 mg Chlorpromazine [CPR], reperfusion 120 min), IV. group - 20 dogs (60 min occlusion, 2 mg Trifluoperazine [TFP] + 120 min reperfusion). CPR or TFP were administered 30 min after the ligation. Effect of drugs was quantified on tetrazolium stained gross sections and studied from physiological, biochemical and ultrastructural points of view. Results reveal that treatment of animals with phenothiazines revealing calmodulin inhibitory action, considerably improved the ultrastructure of myocytes in area at risk and allowed for recovery at least 60 per cent of injured myocytes after restoration of reflow. Ultrastructural findings tightly correlate with physiological and biochemical results.