Rupture of an abdominal aortic aneurysm into the inferior vena cava is uncommon. A classic syndrome of high-output heart failure, continuous abdominal bruit, and renal insufficiency has been described and permits a clinical diagnosis if an aortocaval fistula is considered in the differential diagnosis. Classic signs and symptoms can be misinterpreted and are present in less than 50% of cases. Physicians should consider abdominal ultrasonography and aortography in stable patients, followed by prompt surgical intervention. We report the case of a patient with an aortocaval fistula.