Seventy-one patients (mean age 53 years) were treated with oral propafenone, 900 mg/day, for a mean of 6.6 months. A large spectrum of arrhythmias was encountered, and particular attention was paid to their relation with the autonomic nervous system. Drug efficacy was graded from 1 (no effect) to 5 (complete control) according to the clinical result and Holter recording. This method permitted comparisons to be made between propafenone and 3 other antiarrhythmic agents: quinidine, beta-blockers and amiodarone. Among the 32 patients with supraventricular arrhythmias, 9 cases of vagally dependent atrial flutter and fibrillation were less sensitive to propafenone (mean effect 1.4) than to quinidine (mean effect 2.0) or amiodarone (mean effect 2.3). However, 8 cases of adrenergically dependent atrial tachycardia and fibrillation were more sensitive to propafenone (mean effect 4.1) than to beta blockers (3.0) or amiodarone (mean effect 3.5). In 12 cases of miscellaneous atrial arrhythmias the response to propafenone was intermediate. However, 3 patients with resistant junctional tachycardia were improved with propafenone. Among 42 ventricular arrhythmias, 5 patients with extrasystole who were responsive to quinidine (mean effect 3.8) were also improved with propafenone (mean effect 4.6). Propafenone (mean effect 4.1) was much more effective than quinidine (mean effect 2.4) in treating 8 cases of idiopathic benign ventricular tachycardia and even more successful in treating 13 cases of more severe arrhythmias in diseased hearts (propafenone's mean effect 4.1, quinidine's mean effect 1.9 and amiodarone's mean effect 1.9). Propafenone was less effective (mean effect 3.3) than amiodarone (mean effect 4.0) in 4 cases of severe, adrenergically dependent idiopathic ventricular tachycardia (VT).(ABSTRACT TRUNCATED AT 250 WORDS)