A 3,170-g term male infant was delivered via cesarean section because of failure of labor to progress. Pregnancy had been complicated by polyhydramnios, which was diagnosed by ultrasound. The infant had Apgar scores of 4 and 7 at one and five minutes, respectively, and cyanosis and respiratory distress developed shortly after delivery. Breath sounds were decreased over the left hemithorax, and the heart sounds and cardiac impulse were maximal over the right hemithorax. The second heart sound was loud and single. A grade 3/6 harsh systolic murmur alternated with a rough decrescendo diastolic murmur along the right sternal border to give a "to-and-fro" auscultatory sound.
After endotracheal intubation, a chest roentgenogram (Fig 1) was obtained and arterial blood gas determinations in 100% inspired oxygen demonstrated the following values: pH, 7.32; Pco2, 40 mm Hg; Po2, 38 mm Hg; and base excess, 5.3 mEq. The infant was