The relevance of beta-receptor blockade to ouabain-induced cardiac arrhythmias.

1. (+)-propranolol and (+/-)-propranolol are comparable in their potency as a local anaesthetic on the intact and desheathed frog sciatic nerve.2. (+/-)-propranolol is much more potent than (+)-propranolol as a beta-receptor blocking agent and also more effective than the latter in protecting guinea-pigs against ouabain-induced ventricular fibrillation.3. In isolated rabbit atria (-)-, (+)- and (+/-)-propranolol, and I.C.I. 50172, which has hardly any local anaesthetic activity, greatly reduce the rate of rise of the intracellularly recorded action potential at concentrations which have no significant effect on electrical threshold, contractions, spontaneous frequency, maximum driving frequency, repolarization time or conduction velocity.