Antiarrhythmic efficacy of sotalol--noncardioselective beta-adrenergic blocking agent with class III antiarrhythmic action was evaluated in 34 patients [pts] (mean age 55 +/- 11) with chronic ventricular arrhythmias and coronary artery disease, 38% with previous myocardial infarction. Two schedules of dosing were tested: 3 x 80 mg and 2 x 160 mg during 28 days of therapy. Pts with Lown class II and IV arrhythmia derived from 24-hours Holter recording were assigned. Ventricular premature complexes [VPCs] and couplets reduction by 80% and total elimination of runs defined antiarrhythmic efficacy. Proarrhythmia was defined by four times increase in VPCs, ten times increase in couplets and runs or sustained VT episodes. RESULTS Antiarrhythmic efficacy of two doses of sotalol according to study criterion was: 31% for lower dose (3 x 80 mg) and 24% for higher dose (2 x 160 mg). Overall efficacy for both doses was 55%. According to Morganroth criterion, lower dose was effective in 29% pts and both doses, lower and higher, in 41% pts. According to other commonly used criterion: 70% VPCs reduction, 90% couplets reduction and total elimination of runs, lower dose of sotalol was effective in 32% pts and both doses in 47% pts. Significant reduction of heart rate and prolongation of QT and QTc were observed. In 3 pts QT was prolonged over 500 ms. Proarrhythmia according to Velebit criterion was suspected in one patient after one week of 3 x 80 mg teratment which caused premature cessation of therapy. No significant abnormalities in laboratory values were observed. CONCLUSIONS Antiarrhythmic efficacy of sotalol was comparable to other studies. Its value in pts with malignant ventricular tachyarrhythmias: sustained ventricular tachycardia and ventricular fibrillation requires further studies with higher number of patients.