A 2900-G, FULL-TERM MALE was born to a 24-year-old primiparous woman. Apgar scores were 8 and 8 at 1 and 5 minutes, respectively. At 24 hours of life, he had a grade III/VI systolic murmur at the lower left sternal border and developed circumoral cyanosis. His respiratory rate was 70 beats per minute; oxygen saturation, 70% to 85%. Arterial blood gas showed a pH of 7.45; PCO2, 24; PO2, 35; and base deficit, 5.6. After oxygen therapy was started with a fraction of inspired oxygen (FIO2) of 1.0, arterial blood gas levels were pH, 7.41; PCO2, 34; and PO2, 44. Blood samples were obtained, and ampicillin sodium and gentamicin sulfate were administered. His weight was 2810 g; height, 49 cm; and head circumference, 34.6 cm. Vital signs included a heart rate of 148 beats per minute; respirations, 44 per minute; and blood pressure, 66/31 mm Hg. A holosystolic murmur was heard at the lower left sternal border. An echocardiogram revealed normal cardiac structure and evidence of increased right ventricular pressure with persistent right to left shunting at the foramen ovale and ductus arteriosus.