Twenty-nine infants aged 1–14 days had a ‘favorable’ form of PA/IVS including a well developed outflow tract separated from the pulmonary artery by an imperforated membrane, a tricuspid annulus > 7 mms in diameter and no coronary fistulae. All had deep cyanosis and suprasystemic right ventricular (RV) systolic pressure. They received intravenous prostaglandin (PGE1) and underwent transcatheter perforation of the membrane with a guide-wire, or more recently (6 cases) with a radio-frequency probe, followed by balloon dilation. In 6 cases (21%), we failed to perforate or to dilate. In the other 23 (79%), the RV pressure fell dramatically with an outflow gradient < 30 mmHg. Sixteen (70%) recovered an adequate antegrade RV flow while on PGEl within 1–21 days (m = 8.7 ± 7.4). They are still doing well but 3 of them had a residual infundibular stenosis which did not respond to redilation and had to be operated on. Seven (30%) did not improve despite awidely open RV outflow tract and PGEl had to be replaced by a surgical shunt, with 2 deaths and 510 ng term recoveries. Non fatal complications included ductal injury (2). myocardial perforation (1). necrotizing enterocolitis 12), sepsis (1)In conclusionowing to technical advances such as the use of radiofrequency currents, relief of the outflow obstruction can be obtained in 80% of the neonates with favorable forms of PAlIVS. As soon as the RV has recovered its diastolic function, an adequate forward flow will appear. PGE1 should be infused in the meantime and surgery will be avoided in 61% of the cases.