Primary aortocaval fistula (ACF) is a rare complication of abdominal aortic aneurysm (AAA), occurring in only 4% of ruptured cases and less than 1% of all AAAs. The hemodynamic changes resulting from the major shunt caused by the ACF include a sudden increase in inferior vena caval pressure and volume with renal venous hypertension and a decrease in total peripheral resistance. So, if untreated, it leads to irreversible high output heart failure. Preoperative diagnosis is crucial, as adequate preparation should be made for massive bleeding expected at operation. Successful treatment depends on management of perioperative hemodynamics, control of bleeding from fistula and prevention of thromboembolism. We report two cases of successfully treated spontaneous ACF with a review of the literature.