Objective To observe and analyze the changes in electrocardiograms in patients with type 2 diabetes mellitus for a better knowledge of heart lesion caused by diabetes mellitus. Methods The conventional and dynamic electrocardiograms from 369 patients with type 2 diabetes mellitus were compared with those of the controls without diabetes mellitus who matched the patients in age and gender. Results The mean maximum heart rate (113±8) beats/min in patients with diabetes mellitus was significantly higher than that in the control group (98±8)beats/min, but the mean minimum heart rate beats/min was obviously lower in the former ［(51±10) vs (66±8) beats/min］. The incidence of arrhythmia in patients with diabetes mellitus was significantly higher than that in the controls (1060 vs 331 times/24 h), including the sinus (196 vs 43 times/24 h), the atrial (307 vs 99 times/24 h), the junctional (78 vs 22 times/24 h), the ventricular (301 vs 126 times/24 h) and abnormal conduction (178 vs 41 times/24 h). Moreover, the incidence of ST-T ischemic change in patients with diabetes mellitus was also significantly increased when compared with the controls (221 vs 68 times/24 h for ST, and 192 vs 63 times/24 h for T wave, P