The efficacy and safety of bepridil hydrochloride (HCl) and propranolol HCl monotherapy were investigated in a double-blind, parallel-group crossover study in 75 patients with chronic stable angina pectoris. For the first double-blind segment, both drugs reduced the frequency of weekly anginal attacks and nitroglycerin consumption. On exercise testing, bepridil was significantly more effective in terms of increasing time to angina and total work. Heart rate and ST-segment depression decreased to a greater degree with propranolol than bepridil. Bepridil produced a greater increase in QT interval than propranolol; corrected QT (QTc) interval was increased by bepridil and slightly decreased by propranolol. The incidence of adverse effects was roughly comparable for the two active drugs and higher than that for placebo during washout periods. It was concluded that bepridil, at a mean maintenance dosage of 324 mg/day, was at least as effective as propranolol in improving exercise tolerance--specifically time to angina and total work--and that tolerability of the 2 drugs was comparable. In another study, the efficacy and safety of bepridil combined with propranolol were compared with that of placebo plus propranolol in 56 patients who had not been well controlled on propranolol alone. The addition of bepridil significantly reduced the frequency of anginal attacks and weekly nitroglycerin consumption compared with baseline. The combination of propranolol and bepridil also produced significant improvements in total exercise time, time to angina, and total work compared with baseline. The QTc interval increased significantly from baseline in the bepridil combination group and decreased significantly in the propranolol plus placebo group.(ABSTRACT TRUNCATED AT 250 WORDS)