Sudden death and ventricular tachycardia are known to occur late after correction of tetralogy of Fallot. Abnormal dispersion of the QT interval, ventricular late potentials, and prolongation of the QRS complex, alone or in combination, are useful markers of the risk for such complications. Our present prospective study investigates the time course of appearance of two markers, dispersion of QT and JT, and ventricular late potentials, before and after corrective surgery. Dispersion of QT and JT, and signal averaged electrocardiographic parameters, were determined sequentially in 20 patients before, a mean of 9 +/- 3 days after, and again 35 +/- 11 days post-operatively. Dispersion of QT was already abnormal before surgery in two-fifths of the patients, but increased markedly in the later post-operative period. Ventricular late potentials were absent before surgery and in the immediate post-operative period, but were found in one-fifth of patients 1 month later. We conclude that abnormal dispersion of QT is, to some extent, a fact of the natural history of tetralogy of Fallot, but is significantly amplified by surgery. Ventricular late potentials, on the other hand, are absent before surgery, but appear with some delay after the operation, probably as a result of scarring rather than the surgical incision itself. Long-term follow-up is needed to assess the significance of these findings.