The development of a fistula between the aorta and the right atrium is a relatively rare but well-documented complication after cardiac surgery and proximal aortic dissection, and has a high mortality rate if it is not diagnosed adequately and surgically treated without delay. We report a rare case of extracardiac aorta-right atrial fistula. An 86-year-old woman underwent aortic valve replacement via median sternotomy. Two weeks after surgery, the upper median skin incision reopened, which exposed the sternum and revealed purulent discharge inside the wound. Wound and blood cultures were positive for methicillin-resistant Staphylococcus aureus. The wound was treated, and healed in approximately 2 weeks. Six weeks after surgery, the patient suddenly presented with dyspnea because of heart failure.Extracardiac aorto-right atrial fistula was confirmed by computed tomography. During surgery, we found an extracardiac fistula formed in the hematoma between the sites where the aortic vent suture was tied and the caval cannula was removed. The infection seemed to have contributed to the development of the fistula and may have persisted in the ascending aorta or artificial valve, which may have led to cerebral hemorrhage resulting in death 4 months later.