Time-sequential responses to endothelium-dependent and -independent vasodilators and angiotensin-converting enzyme (ACE) inhibitors were studied in the subendocardial arterioles (ENDO) of canine renovascular hypertension compared with subepicardial arterioles (EPI, both <120µm) by CCD intravital microscope. Vascular responses to acetylcholine, papaverine and cilazaprilat were compared between normotension (N) and hypertension (4wHT and 12wHT). The acetylcholine-induced vasodilation of ENDO in both 4wHT and 12wHT was smaller than that of N (both P<0.01 vs. 4wHT and 12wHT), and that of EPI was smaller than that of N only in 12wHT (P<0.05). The pavpaverine-induced vasodilation of ENDO, but not EPI, was impaired only in 12wHT (both P<0.01 vs. N and 4wHT). The vasodilation by cilazaprilat remained unchanged at 4wHT and 12wHT in both EPI and ENDO. In conclusion, at the early stage, the endothelium-dependent response of ENDO was impaired, while at the later stage, the endothelium-dependent and -independent responses of ENDO, and the endothelium-dependent response of EPI were impaired. However, the vasodilatory responses to the ACE inhibitor were maintained in both ENDO and EPI of hypertension.