The signal averaged electrocardiogram (SA-ECG), programmed electrical stimulation (PES), and left ventricular ejection fraction (EF) studies were utilized for risk stratification and management of patients with complex ventricular arrhythmias and nonsustained ventricular tachycardia (VT). The study population included 90 patients (63 with coronary artery disease and 27 with dilated cardiomyopathy). Sustained monomorphic VT was induced in 22 cases (24%), ventricular fibrillation (VF) in 10 (11%), and no sustained VT/VF in 58 (64%). An abnormal SA-ECG was recorded in 23 patients (26%) and was more common in patients with than in those without induced sustained VT (68% vs 12%, P less than 0.0001). None of 33 patients with normal SA-ECG and EF greater than or equal to 40% had induced VT. Patients were followed-up for 2.5 +/- 0.8 years off antiarrhythmic therapy, unless they had induced sustained VT. The 3-year sudden death rate was 19% in the group with induced sustained VT, 0 in that with induced VF, and 9% in that without induced VT/VF (P = NS). The 3-year total cardiac mortality was higher in patients with than in those without EF less than 40% (27% vs 7%, P less than 0.05). It is concluded that patients with organic heart disease and spontaneous nonsustained VT may not need PES or antiarrhythmic therapy if SA-ECG is normal and EF is greater than or equal to 40%, since their risk of induced VT and sudden death is low. On the other hand, patients with abnormal SA-ECG and/or EF less than 40% may require PES, since their risk for induced VT is high. Antiarrhythmic therapy may also be considered in these patients.