Cardiac hypertrophy and proximal dilatation of the artery have been so frequently associated with arteriovenous fistulas that it has long seemed highly probable that there must be some causative relationship between the two. That such a relation exists has been denied by clinicians, both ancient and modern, and the association of the two conditions clinically has been attributed to a coincidence. It was a problem that aroused the interest of the late Professor Halsted many years ago, and was for him a subject of constant speculation. Speaking before the American Surgical Association1 in 1918. he said: If the assumption is correct that the heart dilates in consequence of the fistula, it is important that the fact should be brought to the attention not only of surgeons but also of pathologists and internists who apparently have altogether overlooked it.... When a causative relationship... shall have become convincingly established, we may