The following clinical findings were seen with increased frequency in patients with idiopathic pulmonary artery dilatation: pulmonary ejection click, systolic ejection murmur in the pulmonic area and abnormally wide splitting of second heart sound. 2. Hemodynamically these patients present often a pressure gradient on the pulmonic valve of minor degree and a slightly elevated cardiac index. A congenitally increased elasticity of the tissue of the common pulmonary artery has to be considered as the possible etiology of this lesion. 3. The diagnosis of idiopathic dilatation of the pulmonary artery can be established by non invasive methods, excluding pulmonary valvular stenosis, pulmonary hypertension and left-to-right shunts.