Ventricular tachycardia (VT) and sudden death are rare but recognized complications after surgical repair of tetralogy of Fallot. We prospectively studied 31 patients (19 boys and 12 girls, mean age +/- standard deviation 7 +/- 4 years) with postoperative tetralogy of Fallot, by means of right-sided cardiac catheterization, 24-hour Holter monitoring, body-surface and intracavitary signal-averaging (gain 10(5) to 10(6), filters of 100 and 300 Hz) and programmed ventricular stimulation (1 and 2 extrastimuli, 3 basic cycle lengths, right ventricular apex and outflow tract). All patients were asymptomatic and none had documented or suspected ventricular arrhythmias. Ventricular late potentials were detected in 10 of 31 patients (32%) and spontaneous ventricular arrhythmias in 12 of 31 patients (39%). No sustained VT was induced by programmed ventricular stimulation but nonsustained VT was induced in 3 patients (10%). Patients with inducible VT more often had late potentials (3 of 3 vs 7 of 28, p less than 0.01), and spontaneous ventricular premature complexes (VPCs) during Holter monitoring (3 of 3 vs 9 of 28, p less than 0.05). To predict VT inducibility, late potentials had a sensitivity of 100%, a specificity of 75%, a positive predictive value of 30% and a negative predictive value of 100%. For spontaneous VPCs, the figures were 100, 68, 25 and 100%, respectively. It is concluded that shortly after repair of tetralogy of Fallot, the presence of both spontaneous VPCs and ventricular late potentials are associated with an increased incidence of inducible VT. Conversely, the absence of VPCs and ventricular late potentials may identify patients at low risk of subsequent ventricular arrhythmias.