Aortocaval fistula is a rare but serious complication of an abdominal aortic aneurysm characterized by communication between the dilated abdominal aorta and inferior vena cava. Prompt diagnosis and treatment are essential to reduce the mortality rate. A 66-year-old man with a history of poorly controlled hypertension, diabetes mellitus, and dyslipidemia presented to the emergency department with sudden, severe lower back pain. Laboratory investigations showed a rapid drop in hemoglobin levels and increased lactate levels. A CT scan revealed an aortocaval fistula resulting from a rupture of the abdominal aorta. The patient underwent emergency surgery, but a cardiac arrest occurred during the procedure, and he could not be resuscitated. Despite advances in imaging and surgical techniques, the mortality rate of aortocaval fistula remains high. It is crucial for clinicians to maintain a high level of suspicion for aortocaval fistula in patients with an abdominal aortic aneurysm who present with a sudden onset of abdominal and back pain and to initiate appropriate resuscitative measures and an urgent surgical consultation.