Two groups of left pulmonary-subclavian artery anastomosis were done in 26 adult mongorel dogs. For the first group. the distal end of the subclnvian artery was nnastomosed to the side of the left pulmonary artery, and for the second group, the subclavian end wns anastomosed to the proximal end of the left lower lobe pulmonary artery. Among them, 6 died of bleeding or anesthetic failure during the day of operation, 10 survived 1 to 106 days and the other 10 were sacrificed at various interval. To investigate the relationship between hemodynamic stress and temporal evolution of the pulmonary vascular lesions. the pulmona try and femoral artery pressures, arteriogram and pathohistological specimens were obtained. The following results were obtained. 1. The postoperative pulmonary artery pressures were within normal limits except 2 dogs in the first group, but in nil 12 dogs of the second group, they were in moderate to maked pulmonary hypertension level. 2 After subclavian pulmonary anastomosis, both groups dogs showed increased femond artery pulse pressure. 3. The pulmonary vascular changes were more severe and appeared earlier in the second group dogs compared with the first group.4. The earliest vascular changes appeared in the media of the small muscular arteries and arterioles. 5. Various vascular chaDges were produced in 2 or 3 months. Thereafter, the changes were stationary.