Arteriovenous fistulas in the mesenteric and portal systems are thought not to produce an increase in systemic blood flow. A case of traumatic superior mesenteric arteriovenous fistula caused an unexpectedly high cardiac output state. Selective angiography was useful in the confirmation and exact localization of the fistula. Hepatic vein wedge pressures in this case were at the upper limit of normal despite increased portal venous flow. Good correlation between portal venous pressure and wedged hepatic vein pressure in many entities causing portal hypertension may not necessarily exist in this hyperkinetic form. © 1973, American Medical Association. All rights reserved.