The surgical results of 9 patients (group II) who were treated for thoracoabdominal aneurysm using left heart bypass combined with oxygenation were compared to those of 16 patients (group I) using left heart bypass without oxygenation. The left heart bypass time in group II was longer than that in group I, and the operations performed in group II were more extensive with more intercostal and lumbar arteries being reconstructed than those in group I. Nevertheless, bleeding associated with transfusion was less in group II than in group I. Intraoperatively, hypothermia and hypoxemia developed in 44% and 31%, respectively of group I, whereas neither of these conditions occurred in group II. There were three operative deaths in group I, compared with one in group II. Paraplegia was encountered in one patient of group I, but in none of the patients in group II. There were a few patients with respiratory failure or other organ failures in both groups. Our results showed that left heart bypass combined with oxygenation offered more stable and effective respiratory as well as circulatory support for a long duration compared to conventional left heart bypass without oxygenation in the surgical treatment of thoracoabdominal aortic aneurysm.