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Nicorandil is a potent coronary vasodilator. To assess its long-term antianginal effect, we designed a randomized, parallel double-blind trial of 6 weeks' duration comparing nicorandil (10 or 20 mg b.i.d.) with propranolol (40 or 80 mg t.i.d.). The study comprised 77 men with stable angina, no maintenance medication at entry, and an exercise test positive for angina and ST-segment depression. The therapy was started with 10 mg nicorandil b.i.d. or 40 mg propranolol t.i.d. After 3 weeks, the dosage could be doubled according to clinical criteria. Four men receiving nicorandil and one receiving propranolol were withdrawn with side effects; in three cases, the data were not complete. Thus, comparative data were obtained in 69 patients; in 51 of these (26 receiving nicorandil and 25 receiving propranolol), the dosage was increased to the higher level. Blood pressure and heart rate were unaltered by nicorandil and lowered by propranolol. The number of anginal attacks decreased relative to baseline on nicorandil and propranolol (p0.002), but total exercise duration was not influenced by either drug. The exercise test performed 2 h after either pill ingestion showed a decrease and a delay in occurrence of myocardial ischemia. The test performed 12 h after medication exhibited reduced ischemia, whereas only propranolol resulted in delayed ST-segment depression. The double product of heart rate and systolic blood pressure was affected only slightly by nicorandil and reduced significantly by propranolol (p0.001). Thus, nicorandil medication affords similar improvement as propranolol in patients with angina pectoris, but the mode of action appears to be different.