INTRODUCTION AND PURPOSES: Propafenone is an antiarrhythmic drug with well known electrophysiological effects. We performed this prospective non comparative study, in order to evaluate its efficacy and safety to terminate spontaneous episodes of monomorphic sustained ventricular tachycardia. METHODS Thirty-two episodes of sustained monomorphic ventricular tachycardia in 32 consecutive patients were treated with intravenous propafenone. Twenty-five were male and 7 female, mean age of 62 +/- 12 years; 23 suffered chronic ischemic heart disease, 2 dilated cardiomyopathy, 1 arrhythmogenic dysplasia of the right ventricle and 6 no organic heart disease. Patients with overt heart failure, acute myocardial infarction or a systolic blood pressure less than 90 mmHg were excluded. The ventricular origin of the tachycardia was assessed by clinical and electrocardiographic criteria and by the presence of AV dissociation in intraesophageal recording. The dose of propafenone was 0.2 mg/kg/min until interruption of ventricular tachycardia, or maximal dose of 2.5 mg/kg in 10 min. RESULTS In 23 episodes (72%) sinus rhythm was restored in less than 10 minutes (mean time and dose, 398 +/- 97 s and 95 +/- 42 mg, respectively). Two patients developed proarrhythmia with acceleration of the ventricular tachycardia. A significant decrease in blood pressure was noted in 6 patients. Presence of organic heart disease, advanced age and poor functional class were the best predictors of inefficacy to convert to sinus rhythm and of the presence of acute adverse effects (p < 0.05). CONCLUSIONS Propafenone is an effective drug for the acute conversion of spontaneous monomorphic sustained ventricular tachycardia, especially in patients without organic heart disease. Age, functional class and presence of organic heart disease could predict the response to propafenone and the incidence of complications.