The authors have investigated in 6 dogs the disturbances of the perfusion determined by ligature of the main left pulmonary artery, of the pulmonary veins, and mixed ligatures. The scintigraphic method was used (consisting in intravenous injection of radionuclide-labelled ferric colloids, and detection with the Anger camera). In 12 dogs electrocardiographic modifications were also investigated, occuring at various intervals of time after the above-mentioned ligatures. With the aid of scintigraphy it was noted that pulmonary perfusion was abolished in the corresponding lung both immediately and at 24 hours following ligatures. With the aid of scintigraphy it was noted that pulmonary perfusion was abolished in the corresponding lung both immediately and at 24 hours following ligature of the vessels. The same aspects was noted in all three types of ligature. Consecutive infarctions were noted at necropsies. The electrocardiogram evidenced sings of coronary failure when all the pulmonary veins of one lung were ligatured, signs of ventricular and atrial overcharge in dogs with ligature of the pulmonary artery and mixed modifications, although less severe, in combined vascular ligatures. The more rapid evolution toward death of dogs with ligatures of the pulmonary veins could be explained by the coronary failure.