During ECC, dogs ventilate spontaneously according to classical physiology. Further, given the CO2 clearance insured by the ECC oxygenator, many hours of reversible apnea are tolerated without sequellae. Surgical removal of the lungs shows that an emptied chest still responds to chemical drives, but the absent lung-recoil causes hyperinflation with lethal failure. Finally, liquid ventilation induces metabolic acidemia through phasic gut ischemia and respiratory muscle strain that destroys the delicate lung structure.