arteriovenous fistula, abnormal direct opening between an artery and a vein; it sometimes results from accidental penetration wounds or from vascular disease, or it may be congenital in origin. As a result of the defect, the arterial blood is passed to the venous side of the fistula, and the blood pressure in the vein increases, causing distension. Symptoms include an aching pain in or beyond the area of the injury and puffy legs that frequently show distended veins. When there is an arteriovenous fistula, the pulse in the vein is diminished by direct compression of the supplying artery, resulting in a continuous murmur that may help in diagnosing and locating the fistula. Normal blood flow can usually be reestablished by surgery.