Survival from reversible forms of severe pulmonary insufficiency remains dismal despite the development of artificial oxygenators. We hypothesized that an intraabdominal heterotopic lung could help maintain adequate oxygenation during acute pulmonary insufficiency. Five mongrel dogs underwent an acute heterotopic lung transplant (HLT). The left atrial cuff was anastomosed to the inferior vena cava, and the left pulmonary artery was anastomosed to the abdominal aorta. The trachea was exteriorized, intubated, and ventilated with a volume-controlled ventilator. Ventilation to the native lungs was discontinued. The heterotopic lung was then ventilated at a rate of 20/min, tidal volume of 15 ml/kg, and inspired concentration (FIO2) of 50 percent. Partial pressure of oxygen (PO2) and mixed venous oxygen saturation (SvO2) were maintained at 53 +/- 5.2 mm Hg and 71 +/- 12 percent, respectively. Flow through the HLT was approximately 20 percent of the systemic cardiac output and did not vary with changes in FIO2, respiratory rate, or positive end-expiratory pressure (PEEP). Four separate animals underwent HLT and were studied 2 to 3 days later. The FIO2 was reduced in the native lungs to 10 percent until SaO2 was less than 90 percent. The HLT was then ventilated at a tidal volume of 300 ml, an FIO2 of 50 percent, and a respiratory rate of 10. Arterial PO2 increased from 62 +/- 4 mm Hg to 75 +/- 2 mm Hg, and SvO2 increased from 75 +/- 2 percent to 82 +/- 3 percent (p < 0.05). Flow through the HLT increased slightly to 27 percent of the systemic cardiac output. We conclude that a HLT can augment oxygenation after induction of moderate hypoxemia, but cannot serve as the sole source for gas exchange because flow through the HLT is limited to less than 30 percent of the cardiac output.