Complete interruption of pulmonary venous return from the left lung in rabbits is compatible in some instances with prolonged survival with little systemic effect. The main cause of death less than 48 hours after interruption of pulmonary venous return is pulmonary-pulmonary aspiration and respiratory insufficiency due to spillover of frothy, bloody fluid, after which infection may play a part. Marked anemia after unilateral pulmonary venous ligation attests to the loss of blood into the lung. Death from unilateral pulmonary venous ligation did not occur if the corresponding main bronchus was ligated to prevent pulmonary-pulmonary aspiration; Despite ligation of the pulmonary veins the corresponding pulmonary artery remained patent.