OBJECTIVES This study reviewed our experience with percutaneous balloon valvotomy in infants with critical pulmonary stenosis or membranous pulmonary atresia with intact ventricular septum and defined the anatomic and hemodynamic characteristics of infants in whom this procedure is successful and provides definitive therapy. BACKGROUND Unlike children with valvular pulmonary stenosis, the follow-up of infants with critical pulmonary stenosis undergoing percutaneous balloon valvotomy is limited. METHODS Between December 1987 and August 1992, percutaneous balloon valvotomy was attempted in 12 infants with critical pulmonary stenosis (n = 10) or pulmonary atresia with intact ventricular septum (n = 2). Two outcome groups were identified: Group A patients are acyanotic, have mild residual pulmonary stenosis and have not required operation; Group B patients have required operation. RESULTS Of the 12 infants, 11 had a successful balloon valvotomy procedure. Group A patients (n = 7) have a residual gradient of 22 +/- 18.7 mm Hg (mean +/- SD) at follow-up of 3.2 years (range 1.2 to 5.0). In Group B (n = 5), operation was required for inability to cross the pulmonary valve (n = 1) or persistent severe hypoxemia for > or = 2 weeks after valvotomy (n = 4). Significant differences (p < or = 0.01) between the two groups (Group A vs. Group B) were identified in pulmonary valve annulus (Z value) 8.1 mm (-1.1) versus 5.5 mm (-3.4); tricuspid valve annulus (Z value) 14.0 mm (0.8) versus 8.8 mm (-1.8); right ventricular volume 65 versus 29 ml/m2; and Lewis index 10.9 versus 8.9. CONCLUSIONS Percutaneous balloon valvotomy is effective and likely to provide definitive therapy in infants with critical pulmonary stenosis or membranous pulmonary atresia with intact ventricular septum who have a tricuspid valve annulus > 11 mm, pulmonary valve annulus > or = 7 mm and right ventricular volume > 30 ml/m2.