The patient was a 69-year-old man brought to the emergency room with severe chest pain. A contrast chest CT scan revealed a hematoma around the ascending aorta and a notch in the aortic wall, suggesting an intimal tear. An emergency operation was performed via standard median sternotomy under deep hypothermic circulatory arrest. Upon operation, there was a 2.0 cm intimal tear just above the right coronary leaflet, which was extended near the right coronary artery orifice. There was no specific evidence of aortic aneurysm or dissection, therefore a spontaneous rupture of the ascending aorta was diagnosed. The pathological finding was cystic medial necrosis Grade 2. His postoperative course was unremarkable and he was discharged 12 days after surgery.