Regression of infundibular pulmonary stenosis after successful balloon pulmonary valvuloplasty in adults. Between July 1985 and March 1988, 22 adult patients with congenital pulmonary stenosis underwent balloon pulmonary valvuloplasty. There were 10 males and 12 females aged 16-45 (average 25 +/- 9.9) years. All patients had additional mild to severe infundibular stenosis; 16 were restudied 6-36 (mean 12.6) months later by repeat catheterization. Student's t-test was used for comparison of data. Right ventricular (RV) systolic pressure before dilatation was 84-196 (mean 129 +/- 32.3) mm Hg, and the peak pulmonary gradient (PPG) was 60-176 (mean 111 +/- 33.2) mm Hg immediately after dilatation. The RV systolic pressure dropped to 32-140 (mean 59.2 +/- 27) (P less than 0.001); and PPG dropped to 10-113 (mean 37.8 +/- 26.4) (P less than 0.001), and the infundibular gradient ranged from 8 to 113 (mean 35.1 +/- 25.8) mm Hg. The infundibular diameter, before dilatation, ranged from 2 to 15 (mean 9.5 +/- 4) mm Hg. At repeat catheterization, the RV systolic pressure dropped further to 33-66 (mean 42.8 +/- 9.7) mm Hg and the PPG was reduced to 0-48 (mean 18.4 +/- 10.9) mm Hg (P less than 0.001). The infundibular gradient regressed to 0-34 (mean 15 +/- 8.8) mm Hg (P less than 0.001). The infundibular diameter increased to 8-25 (mean 15.8 +/- 5.4) (P less than 0.001). It is concluded that moderate to severe infundibular stenosis, in adults, can regress after successful pulmonary valvuloplasty. 