Aim: We report the case of a large spontaneous retroperitoneal hemorrhage in a patient receiving a heparin infusion. He was treated by blood transfusion, reversal with protamine, and angioembolization. Background: Spontaneous retroperitoneal hemorrhage can present as a rare life-threatening event characterized by sudden onset of bleeding into the retroperitoneal space, occurring in association with bleeding disorders, tumors, or anticoagulation. Case description: We report the case of a patient with central cord syndrome who was treated with heparin infusion for upper limb deep vein thrombosis. This was complicated by a large spontaneous retroperitoneal hemorrhage, which was treated by blood transfusion, reversal with protamine, and angioembolization. Retroperitoneal bleeding is a medical emergency that is often difficult to diagnose due to its rarity and the nonspecific symptoms with which it presents. Treatment may vary. In our case, blood transfusion, reversal of heparin with protamine, and interventional treatment were performed as active bleeding was recognized on angiography. Conclusion: Idiopathic retroperitoneal hemorrhage is an uncommon condition that may lead to shock if not promptly recognized. Timely diagnosis and treatment help improve outcomes. Clinical significance: This is a rare and challenging complication. Timely diagnosis requires high clinical suspicion. Management depends on hemodynamic stability. This case highlights the importance of early detection and treatment and opens the door for more studies to minimize related complications.