Diabetic patients with ischaemic heart disease have a greater liability of myocardial ischaemia, and an in­creased incidence of heart failure compared to the non-diabetic ones. The goal of this study was to clarify the effects of trimetazidine on the ar­chitecture of the myocardium of dia­betic rats. Thirty adult male albino rats (200-250 gm) were used in this investigation. They were divided into three equal groups; control, diabetic non-treated and diabetic TMZ- treat­ed. At sacrifice, small pieces of the myocardium of left ventricle were pro­cessed for histological, histochemical and immunohistochemical study. Myocardium of diabetic rats showed an apparent increase of endomysium. The muscle fibers showed areas of degeneration. Ultrastructu rally, the cardiac myocytes of diabetic rats showed distortion of cardiac myofi-brils with loss of cross banding in many areas. The nucleus had a cor­rugated nuclear membrane and the mitochondria were swollen and dis­torted. Histochemically, myocardium of diabetic rats exhibited a weak suc-cinic dehydrogenase reaction and a strong positive immunoreaction for NF-kappa B and caspase-3 in myo­cardial sarcoplasm. On the other hand, TMZ- treated diabetic rats showed an improvement in the histo­logical architecture and in both histo­chemical and immunohistochemical reactions. So, TMZ should always be advised for diabetic patients to allevi­ate the cardiac hazards.