AIM: To observe the efficacies characteristic and side effects of sotalol in controlling chronic refractory ventricular premature contraction (VPC) and in preventing the attacks of symptomatic paroxysmal atrial fibrillation (PAF). METHODS: Sotalol was given to 28 patients with chronic VPC and 16 patients with PAF. The initial doses were 120-160 mg/d and increased to the maximum of 320 mg/d in steps if ineffective. The therapy lasted 4 wk for VPC and 8 wk for PAF. The 24 h Holter monitoring and the standard electrocardiogram was used as criterion of effectiveness. RESULTS: The efficacy rates for VPC and PAF were 78 6% and 31 3% respectively. The therapy resulted in marked decrease in both systolic blood pressure and heart rate, and significant prolongation of QT and QTc intervals, and also apparent decrease of QT dispersion but the extent of which being insignificantly different between effective and ineffective patients. No worsening of arrhythmia was found but persistent sinus bradycardia was noted in 13 6%(6/44) of all the patients. The only patient with chronic congestive heart failure in the group showed deterioration in global function during the wk 2 of treatment on 160 mg/d. Other side effects were minor. CONCLUSION: Low to moderate doses of sotalol are reliable in controlling refractory VPC and can be used as first line drug, but being weak in maintaining sinus rhythm in PAF.