In the past few years disturbances of the pulmonary circulation have been studied with renewed interest, and the term pulmonary hypertension has gained more universal usage. The relative obscurity to which the pulmonary arterial tree has been relegated can be attributed to the following causes: (1) its inaccessibility during life, (2) the lack of accurate anatomic criteria whereby pathologic changes in the different parts of the pulmonary arterial tree can be correctly evaluated at necropsy and (3) the similarity of the clinical manifestations of diseases of the pulmonary arterial tree to those of cardiac diseases and pulmonary disturbances. The name Ayerza's disease is closely linked with diseases of the pulmonary artery. This term has had an interesting influence on the conception of diseases of the pulmonary artery. According to Brenner,1in the case originally discussed by Ayerza, in which the patient was described as a black "cardiac," necropsy disclosed