These cases are of interest because they are clear examples of an uncommon complication of aortic aneurysm. In both instances the physical signs were similar and so distinctive as to be pathognomonic of internal arteriovenous aneurysm. The recorded cases presenting an abnormal communication between the root of the aorta and the pulmonary artery may be separated into two distinct groups. In one, the aorta is not diseased, and the opening between it and the pulmonary artery is due to a developmental defect in the wall between the two great vessels. In a few instances, the opening is congenital; in others, it occurs spontaneously at the site of a small aneurysm involving the right anterior aortic sinus of Valsalva. Such a case was recently reported by Abbott,1who summarizes the eight previously recorded cases, and presents a critical discussion of the subject from the embryologic and comparative anatomic point of