Antiarrhythmic properties of 5-(3-tert-butylamino-2-hydroxy)propoxy-3,4-dihydrocarbostyril hydrochloride (OPC-1085), a newly synthesized, potent beta-adrenoreceptor antagonist.

1. The antiarrhythmic properties of 5-(3-tert-butylamino-2-hydroxy)propoxy-3,4-dihydrocarbostyril hydrochloride (opc-1085) were compared with those of propranolol and pindolol using various kinds of preparations for experimental arrhythmia in dogs. 2. Although OPC-1085 was the most potent drug to antagonize adrenaline-induced arrhythmia in animals anaesthetized with either pentobarbitone sodium or halothane, it was scarcely effective on ouabain-induced arrhythmia in pentobarbitone sodium anaesthetized animals. 3. When these compounds were administered intravenously to conscious dogs 24 h after two-stage ligation of the anterior descending artery, ectopic ventricular beats of coronary ligation-induced arrhythmia were reduced while regular sinus beats were simultaneously increased. 4. OPC-1085 was very effective on aconitine-induced arrhythmia in dogs anaesthetized with pentobarbitone sodium. The effective dose was similar to that of propranolol but about fifteen times less than that of pindolol. 5. It is concluded that different potencies among these beta-adrenoreceptor antagonists against various kinds of experimental arrhythmias cannot be simply deduced from any one of the following properties; beta-adrenoreceptor antagonism, intrinsic myocardial stimulation, local anaesthetic and so-called quinidine-like effects.