Blade atrial septostomy was performed in 18 patients, including 14 with transposition of the great arteries, three with tricuspid atresia and one with severe mitral stenosis and ventricular septal defect. The patients' ages ranged from 25 to 210 days (mean: 108 +/- 64 days), and weights ranged from 3.0 to 6.0 kg. Following blade septostomy, partial arterial pressure of oxygen (PaO2) increased from an average of 22 +/- 3.3 mmHg to 38.9 +/- 7.6 mmHg (p < 0.001), and prompt clinical improvement was observed in the majority of patients. Significantly decreased atrial pressures (from 8.16 +/- 6.1 to 3.93 +/- 2.2 mmHg, p < 0.01) and significantly enlarged inter-atrial openings (from 1.6 +/- 0.9 to 7.5 +/- 1.8 mm, p < 0.001) were achieved with successful blade atrial septostomy. Blade atrial septostomy is an effective and life-saving procedure in patients who require nonrestrictive inter-atrial communication.