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Since 1983 percutaneous balloon dilatation of the right ventricular outflow tract has been performed as an alternative to surgical palliation in selected cases of tetralogy of Fallot at the Royal Liverpool Children's Hospital. From 31 December 1984 to 31 December 1988, 27 of these patients underwent subsequent surgical correction. Age at operation ranged from 7 to 58 months (median 2-7 years). The mean interval between balloon dilatation and correction was 15-6 months (range 3-39 months). Two patients had a systemic pulmonary shunt operation performed before dilatation and a further five required one afterwards. Overall 20 (74%) patients had some anatomical alteration as the result of balloon dilatation, while in seven (26%) there was no discernible change in the right ventricular outflow tract. There was no consistent relation between the ratio of balloon size to pulmonary annulus diameter and the morphological findings.Balloon dilatation may obviate the need for systemic-pulmonary shunt at the expense of some structural damage, particularly to the posterior cusp. The present data suggest that dilatation does not bring about growth of the annulus to such an extent that transannular patch is no longer needed at intracardiac repair. The median age of the patients at operation was 33 months (range 7-58 months). Twenty one of them had one pulmonary dilatation, four had two procedures, and two patients had three and four balloon dilatations. The mean age at the first dilatation was 10-0 months (range 0-5-30); for all dilatations the median age was 14-6 months (range 0-5-56). Balloon sizes ranged from 5 to 15 mm (mean 13 mm). Surgical correction was undertaken 3 to 39 months (mean 15 6 months) after dilatation.At operation the surgeon classified the pulmonary valve leaflets as follows: (a) intact, when there was no observable effect of dilatation; (b) detached, when the leaflet was separated from its hinge-point for a variable length, starting from one of the commissures; (c) split, when a vertical tear was found, usually in mid-portion of the leaflet dividing it in two segments (in no case was a split identified at a commissure); (d) fused, when the leaflets were fused to the pulmonary artery wall, probably after initial detachment.The pulmonary ventriculo-arterial junction (pulmonary annulus) was described as: (a) intact, where there was no observable effect of dilatation; or (b) split, when there was a tear usually originating at the hinge-point of the leaflet and extending a variable distance into the main pulmonary artery and its right branch.The computerised records of all the other patients ( 1 13

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