In experiments on isolated rat and rabbit right atrium, a new class III antiarrhythmic drug RG-2 (0,01-1 microM) was shown to have anticholinergic action competing with 0.2-1 mM carbachol. RG-2 (0.1-1 microM) produced dose-dependent increase of APD90% in rat and rabbit atrial cells and had no effects on other action potential parameters. In presence of carbachol RG-2 produced significantly greater increase of APD90% and caused significant increase of APD50%. Thus RG-2 exerts anticholinergic action, which can take important part in RG-2 antiarrhythmic activity.