Sotalol is a beta-blocking agent endowed with class III electrophysiological properties. It has proved clinically effective in the treatment of arrhythmia, but episodes of torsades de pointe have been observed, particularly (though not exclusively) in the presence of hypokalaemia. The effect of sotalol with or without hypokalaemia was studied on a recently developed model for experimental torsades de pointe. Conscious dogs with complete atrioventricular block (ventricular cycle RR = 1530 +/- 170 ms) and provided with permanent atrial and ventricular epicardial electrodes were given sotalol intravenously either as a 4.5 mg/kg bolus injection or as a 1.5 mg/kg/h infusion. Group I dogs (n = 8) had normal blood potassium levels (4.3 +/- 0.1 mEq/1); following sotalol (plasma concentration 3.7 +/- 0.2 micrograms/ml) the ventricular rhythm was electrically driven to 25/min (RR = 240 ms) and QT was increased by 68 +/- 11 ms; torsades de pointe occurred in 5/8 animals (62 p. 100). Group II dogs (n = 6) had diuretic-induced hypokalaemia (2.6 +/- 0.1 mEq/1); following sotalol (plasma concentrations 3.8 +/- 0.3 micrograms/ml) the ventricular rhythm also depended on an external pacemaker to reach 25/min (in all but 1 dog) and QT increased by 46 +/- 11 ms; torsades de pointes were obtained in 5/6 animals (83 p. 100). These torsades de pointe were prevented in every case by rapid ventricular pacing (100-120/min). Thus, the pro-arrhythmic effects of sotalol were very frequent on this experimental model, but hypokalaemia was not necessary for torsades de pointe to occur.(ABSTRACT TRUNCATED AT 250 WORDS)