Ventricular repolarization analysis has been shown to be effective in the identification of electrical myocardial instability leading to ventricular arrhythmias. The aim of the present study was to examine ventricular repolarization time indexes, in terms of both absolute measures and dispersion across the myocardium, in young patients with repaired tetralogy of Fallot (41 pts; 28M/13F, age 11.7+/-3.6 years), assessing, furthermore, the possible influence of known negative prognostic factors relative to the surgical operation and residual haemodynamic abnormalities. The data of the study group were compared with those of 33 aged-matched asymptomatic control subjects (22M/11F, age 11.7+/-2.3 years). Ventricular depolarisation, as expressed by QRS duration, resulted significantly longer in total Fallot group than in the Control group (P<0.0001). Particularly, patients operated through a right ventricular approach showed higher values of QRS interval (P<0.0001) than those operated through a combined transatrial-transpulmonary approach. All the patients operated on for tetralogy of Fallot exhibit, with respect to control subjects, an inhomogeneous prolongation of ventricular repolarization across the myocardium, as showed by the significant increase in the absolute indexes of ventricular repolarization, JTc (P<0.001), QT (P<0.0001) and QTc (P<0.0001) with a concomitant prolongation of the indexes of dispersion of ventricular recovery time, QTcD (P<0.0001), JTcD (P<0.0001), 'adjusted' QTcD (P<0.001) and Tp-Te interval (P<0.0001). A temporal and regional variation in the ventricular repolarization across the myocardium in patients with repaired tetralogy of Fallot, could create the pathophysiological substrate for an increased cardiac electrical instability. The presence of negative prognostic factors, relative to the surgical intervention or residual haemodynamic abnormalities, even if not influencing the arrhythmic substrate, invariably present, could determine 'trigger' conditions essential for the development of ventricular arrhythmias.