Fifty-nine patients operated for Fallot's tetralogy were reviewed over 3 years after surgery. The average age at surgery was 7.4 years (range 6 months to 37 years). The review included ECG, chest X-ray, echocardiography, exercise stress testing and Holter monitoring, completed by cardiac catheterisation in 10 cases and electrophysiological investigation in 4 cases. Forty-eight of the 59 patients (81.3 p. 100) had no signs of ventricular arrhythmia or only benign ventricular extrasystoles (Group I). Four patients (6.8 p. 100) had severe ventricular arrhythmias (Group II). Seven patients (11.9 p. 100) had one or more episodes of ventricular tachycardia (VT) (Group III) and, in 3 of these patients, VT was recorded during Holter monitoring or exercise stress testing. One patient in Group III died after reoperation, but there were no cases of sudden death in this series. The high risk patients Groups II and III) were operated late (after 5 years), had bi- or trifascicular block (7 out of 11 cases), ventricular extrasystoles on resting ECGs (9 out of 11 cases), cardiomegaly (6 out of 7 cases in Group III), echocardiographic dilatation of the infundibulum (6 out of the 8 patients undergoing echocardiography in Groups II and III). They had significant residual malformation but without right ventricular hypertension (as judged mainly by immediate postoperative data). Ventricular arrhythmias occurred over 6 years after surgery. However, none of the patients operated before 2 years of age had ventricular arrhythmias or VT with a mean follow-up period of 7.5 years, perhaps because LV function was protected.(ABSTRACT TRUNCATED AT 250 WORDS)