The placement of a Swan-Ganz catheter into the abdominal vena cava by the femoral route is recommended for all patients presenting with severe congestive heart failure and an abdominal aortic aneurysm. If an aortocaval fistula exists, its presence can be determined immediately by noting increased vena caval pressure and higher than normal oxygen content. Immediate recognition of this condition is essential. Fluid overloading is avoided, immediate surgical treatment is instituted and the defect is closed. Minimal manipulation is done in an effort to prevent pulmonary embolization. If the results of catheter studies show no evidence of an aortocaval communication, it may be advisable to make an effort to correct the congestive heart failure before surgically correcting the aneurysm.