Abstract: AIM To investigate the therapeutic effects of enalapril and diltiazem on patients with cardiac X-syndrome. METHODS Forty-three patients with cardiac X-syndrome were randomly allocated to be treated by enalapril (Group A, n=21) and diltiazem (Group B, n=22) for three months. The clinical presentations, results of treadmill tests, coronary flow reserve (CFR), and the levels of endothelin-1(ET-1) and nitrooxide (NO) were compared before and three months after treatment. RESULTS After the 3-month therapy, chest pain, ST depression and the levels of ET-1 significantly decreased and CFR, the levels of NO significantly increased and total exercise duration, time to 1 mm ST segment depression were significantly longer (P<0.01 or P<0.05, vs before treatment) in the two groups. Chest pain, ST depression and the levels of ET-1 significantly decreased, CFR and the levels of NO significantly increased (all P<0.05 vs diltiazem group) and total exercise duration and time to 1 mm ST segment depression were significantly longer (all P<0.05 vs diltiazem group) in enalapril group. CONCLUSION Enalapril may have a better effect than diltiazem in the improvement of exercise tolerance for the patients with cardiac X-syndrome.