A 78-year-old man with a history of hypertension was admitted for a fall with back pain. The blood pressure was at 110/50 mmHg and the pulse at 115 b.min-1. A pulsatile abdominal mass was palpated. No signs of respiratory insufficiency or congestive heart failure were found. The diagnosis of abdominal aortic aneurysm was promptly confirmed by echography. Before laparotomy, a pulmonary artery catheter was inserted for haemodynamic monitoring which showed a high cardiac output, low systemic vascular resistances, increased pulmonary artery wedge pressure and a high SvO2 (93%). This was not consistent with a hypovolaemic shock but rather an aortocaval fistula. After incision and aortic clamping, surgical procedure consisted of transaortic closure of the fistula and restoration of arterial continuity with a prosthetic graft. Initial control of venous bleeding was obtained by passing a Foley's catheter distally and by clamping the vena cava. The postoperative course was initially satisfactory. The patient was extubated, but remained with a major renal insufficiency. After a stay of 15 days in the intensive care unit, he died from nosocomial pneumonia. Aortocaval fistulas are either traumatic or spontaneous. Spontaneous fistulas are more common, and in about 90% of the cases result from a rupture of an atherosclerotic aortic aneurysm. Clinical findings include signs of high cardiac output symptoms of venous hypertension and regional arterial insufficiency. Haemodynamic changes can be of value for the recognition of an aortocaval fistula. Most authors emphasize the importance of preoperative diagnosis, allowing the use of appropriate operative techniques and a prompt control of the fistula. This could decrease haemodynamic instability and transfusion requirements.