Percutaneous balloon pulmonary valvuloplasty was performed in seven children with moderate to severe valvular pulmonary stenosis (right ventricular to pulmonary artery pressure gradient greater than 50 mm Hg). All patients experienced a decrease in right ventricular peak systolic pressure from 108 +/- 30 to 60 +/- 5.6 mm Hg (p less than 0.001), decrease in right ventricular to pulmonary artery gradient from 90.1 +/- 30 to 38.8 +/- 5 mm Hg (p less than 0.001) and increase in pulmonary valve area from 0.33 +/- 0.06 to 0.55 +/- 0.15 cm2/m2 (p less than 0.001). In the two patients who underwent supine bicycle exercise before and after valvuloplasty, a significant decrease in both the maximal right ventricular peak systolic pressure (212 to 140 and 175 to 125 mm Hg, respectively) and in right ventricular to pulmonary artery peak pressure gradient (185 to 110 and 151 to 85 mm Hg, respectively) occurred. All patients tolerated the procedure well and no serious complications were observed. It is concluded that percutaneous balloon valvuloplasty is a safe and effective method for relief of right ventricular obstruction due to moderate or severe valvular pulmonary stenosis. However, long-term results remain unknown.