The percutaneous balloon valvulotomy is nowadays the treatment of choice for isolated pulmonary stenosis. Forty two patients with congenital pulmonary stenosis underwent balloon valvulotomy at the Instituto Nacional de Cardiología "Ignacio Chávez". Ages 1 month to 24 years, mean 7.6 +/- 5.9 years, with a follow-up of 28.3 +/- 14.8 months. With an infundibular gradient of 50 mm Hg or more a treatment with propranolol was given. After valvulotomy the total basal pressure gradient decrease from 82.9 +/- 40.6 mm Hg to 31.2 +/- 27.1 mm Hg (p < 0.00001). The patient's results were divided in two groups: with and without reactive infundibular obstruction. The 31 patients without infundibular obstruction had a total initial gradient of 71.6 +/- 33.5 mm Hg, and after valvulotomy the gradient was reduced to 18.9 +/- 11.2 mm Hg (p < 0.00001). The 11 patients with infundibular obstruction had a total initial gradient of 114.8 +/- 43.2 mm Hg, and after valvulotomy the valvular gradient was 12.4 +/- 8.5, the infundibular gradient 53.4 +/- 22.9 and the total gradient 65.9 +/- 29.1 mm Hg (p = 0.002 in relation to the basal gradient). All patients with infundibular obstruction (8 treated with Propranolol) and a follow-up of 8.5 +/- 9.8 months underwent Doppler examination, showing a progressive reduction of the total gradient. By six months no one had a total gradient greater than 50 mm Hg. These data confirm that balloon valvulotomy in valvular pulmonary stenosis is safe and effective, and that restenosis is very low. Good results relay on the use of proper balloon diameters (balloon diameter/pulmonary annulus relation of 1.2 to 1.5).(ABSTRACT TRUNCATED AT 250 WORDS)