Percutaneous balloon aortic valvuloplasty (BAV) was performed in 23 consecutive patients with valvular aortic stenosis with no associated cardiac defects. The patients were 2 to 17 years old and were referred from 12 hospitals in 4 states. The balloon was positioned across the aortic valve and inflated to pressures of 80, 100, then 120 psi. Each inflation lasted 5 to 10 seconds. The arterial and venous catheters were connected together outside the groin to avoid excessive increase in left ventricular pressure during total aortic valve occlusion with the inflated balloon. Peak systolic aortic valve pressure gradient and cardiac output were measured before and 15 minutes after BAV. There was no significant change in cardiac output, but all patients had a lessened gradient. The gradient before BAV was 113 +/- 48 mm Hg, decreasing to 32 +/- 15 mm Hg after BAV (p less than 0.01). The left ventricular peak systolic pressure decreased from 221 +/- 54 to 149 +/- 21 mm Hg (p less than 0.01). No aortic regurgitation was noted in 13 patients and very mild aortic regurgitation was noted in 10 patients after BAV. The balloons were 10 to 20 mm in diameter, chosen at least 1 mm smaller than the diameter of the aortic valve anulus. Pressures of 100 to 120 psi were required to achieve full inflation of the balloons. Six patients had repeat cardiac catheterization studies 3 to 9 months after BAV. In none was there a significant change in peak systolic aortic valve pressure gradient or cardiac output compared with the study immediately after valvuloplasty.