Myocardial ATP-sensitive potassium (K(ATP)) channels have been implicated in attenuating cardiac hypertrophy by modulating endothelin-1 concentrations. Sulfonylureas differ in their affinity for cardiac K(ATP) channels and therefore may vary in their effects on left ventricular (LV) mass. We sought to determine the differential effects of sulfonylureas on LV mass in type 2 diabetic patients. All patients had been taking glibenclamide for more than 3 mo before being randomized to either switch to an equipotent dose of gliclazide or continue glibenclamide. A total of consecutive 240 diabetic patients were randomized into glibenclamide, gliclazide, a combination of glibenclamide and nicorandil, or gliclazide and nicorandil for 6 mo. In the gliclazide-treated group, the LV mass index was significantly decreased compared with that in the glibenclamide-treated groups. Nicorandil administration significantly reduced LV mass in glibenclamide-treated patients compared with patients treated with glibenclamide alone. Measurements of endothelin-1 concentrations mirrored the functional status of K(ATP) channel. Multivariate analysis revealed that regression of LV mass was significantly correlated only with the changes in endothelin-1 (P < 0.0001). Our results show that K(ATP) channels may play a pathogenetic role, probably through an endothelin-1-dependent pathway, in diabetes mellitus-related ventricular hypertrophy. Patients treated with gliclazide may have a beneficial effect in attenuating ventricular mass.