In patients more than 65-year-old with diabetes mellitus, positive late potentials on signal-averaged electrocardiograms were more common than in normal subjects (p < 0.05). This suggests that aged patients with diabetes mellitus are at risk for micromyocardial impairment. Myocardial scintigraphy with 123I-metaiodobenzylguanidine showed abnormally low uptake, in parallel with the data on SA-ECG. Thus, both methods may be clinically useful ways to noninvasively reveal micromyocardial impairment in aged patients with diabetes mellitus. Moreover, trimetazidine hydrochloride may be effective as therapy for micromyocardial impairment: the uptake of 123I-metaiodobenzyl guanidine had increased in some patients when measured 1 year after administration of trimetazidine hydrochloride (18 mg/day) and the late potential changed from positive to negative.