Clinical trials suggest that sulphinpyrazone reduces the incidence of sudden death in patients having suffered a myocardial infarction. To investigate possible direct antiarrhythmic properties of sulphinpyrazone, we carried out experiments on spontaneously beating and electrically stimulated isolated rat atrial preparations. Dose-response curves for electrophysiological and mechanical effects of sulphinpyrazone were obtained. Increasing doses of sulphinpyrazone decreased the spontaneous atrial frequency, prolonged the sinus node recovery time after overdrive pacing, slightly increased the electrical threshold for excitation and decreased the contractile force. Although the mechanism by which sulphinpyrazone may reduce the incidence of sudden cardiac death is still not settled, the present study demonstrates direct electrophysiological and mechanical effects of the drug at high concentrations.