Approximately one hundred and forty-two Trendelenburg operations for massive pulmonary embolism have been reported, and only nine of the patients operated on have left the hospital as cured.1 This exceedingly high mortality is due to the critical condition of the patient and to the operative procedure, which entails the complete throttling of the great vessels leading from the heart for a brief period. Because of the difficulty in diagnosis and the uncertain prognosis, Nyström2 advised postponing the operation until the patient is practically moribund. Then, as Churchill3 has stated, "the procedure could perhaps be more properly termed an immediate postmortem examination than a surgical operation."
Nyström and Blalock4 have demonstrated experimentally that occlusion of the pulmonary artery alone may be safely maintained for a longer period than occlusion of both the pulmonary artery and the aorta. Kiser1 found that constriction of the afferent vessels of