The efficacy of propafenone, a new antiarrhythmic drug, was studied in 21 patients with ventricular arrhythmias refractory to previous antiarrhythmic medications. Group A included 10 patients with chronic ventricular premature complexes (VPCs), 6 of whom had nonsustained ventricular tachycardia (VT) and 4 of whom had recurrent, sustained VT; all received propafenone, 900 mg/day. Group B included 11 patients, all with chronic VPCs, 9 of whom had nonsustained VT and 5 of whom had sustained VT; all received propafenone, 450 mg/day. Drug efficacy was evaluated as a 70% or greater reduction in VPC frequency with complex VPC abolition in ambulatory monitoring and suppression of nonsustained VT and sustained VT during a follow-up period up to 154 +/- 58 days in group A and 96 +/- 42 days in group B. Drug plasma levels were measured during chronic therapy in pharmacologic steady state. In group A, propafenone reduced the frequency of chronic VPCs in 9 patients and abolished nonsustained VT in 4 of 6 and sustained VT in 3 of 4; in group B, propafenone reduced the frequency of chronic VPCs in 6 patients and abolished nonsustained VT in 6 of 9 and sustained VT in 3 of 5. Two patients with recurrences of sustained VT in this group were later successfully treated with propafenone, 900 mg/day; overall, 8 of 9 patients with recurrences of sustained VT were successfully treated with 900 mg/day.(ABSTRACT TRUNCATED AT 250 WORDS)