Abstract: AIM: To investigate the effects of benazepril and diltiazem on patients with cardiac X-syndrome. METHODS: Forty five patients with cardiac X-syndrome were randomly allocated to be treated with benazepril (Group A, n=22) or with diltiazem (Group B, n=23) for 3 months. Clinical presentations, results of treadmill tests, coronary flow reserve (CFR), and levels of endothelin-1 (ET-1) and nitric oxide (NO) were compared before and 3 months after treatment. RESULTS: After the 3-month treatment, the number of episodes of chest pain, ST depression and levels of ET-1 significantly decreased (all P<0.01 vs. before treatment). CFR, as well as NO levels, significantly increased (all P<0.01 vs. before treatment) and total exercise duration as well as time to 1 mm ST segment depression were significantly longer (all P<0.01 vs. before treatment) in benazepril group. After the 3-month treatment, the number of episodes of chest pain, ST depression and levels of ET-1 significantly decreased (all P<0.05 vs. before treatment), CFR significantly increased (P<0.05) and total exercise duration as well as time to 1-mm ST segment depression were significantly longer (all P<0.05 vs. before treatment) in diltiazem group. The number of episodes of chest pain, ST depression and the levels of ET-1 significantly decreased and CFR as well the levels of NO significantly increased (all P<0.05 vs. diltiazem group) and total exercise duration as well as time to 1-mm ST segment depression were significantly longer (all P<0.05 vs. diltiazem group) in benazepril group. CONCLUSION: Benazepril may exert a more positive effect than diltiazem in the improvement of exercise tolerance for patients with cardiac X-syndrome.