The pulmonary vessels reflect in their structure the stresses to which they are subjected. Over the years a variety of techniques have been applied to the study of the pulmonary circulation to acquire a greater understanding of the alterations occurring in various diseases. Congenital heart disease has been of particular interest since it may impose unusual hemodynamic stresses upon the vessels of the lungs. For over two decades we have had the opportunity, first at Yale-New Haven Hospital, New Haven, Connecticut and then at University Hospital, San Diego, California, to study the pulmonary...