Percutaneous balloon pulmonary valvuloplasty (BPV) was performed in 18 consecutive patients with valvular pulmonary stenosis (PS) with no associated cardiac defects. The patients were 11 months to 19 years of age. The balloon was positioned across the pulmonary valve and inflated to pressures of 80, 100, and 120 pounds/square inch (psi). Each inflation lasted approximately 10 seconds. Peak systolic pulmonary valve gradient (delta P) and cardiac output were measured before and 15 minutes after BPV. There was no change in cardiac output, but all patients had an improved delta P. The prevalvuloplasty delta P was 81 +/- 31 mm Hg, decreasing to 23 +/- 11 mm Hg after BPV (p less than 0.01). The right ventricular peak systolic pressure decreased from 106 +/- 31 to 50 +/- 12 mm Hg (p less than 0.01). No pulmonary regurgitation was noted after BPV. The balloons were 12 or 15 mm in diameter, chosen according to the diameter of the pulmonary valve anulus. Pressures of 100 to 120 psi were required to achieve full inflation of the balloons. BPV also was performed in a patient with tetralogy of Fallot. Subsequent total repair provided an opportunity to observe the mechanism of the dilatation. Evidence of a small tear alongside the anterior valve raphe was noted. BPV induced a significant decrease in delta P and may offer an alternative method for treating PS.