A 51-year-old woman was operated on for aortic valve regurgitation 3 months after experiencing chest tightness awakening her from sleep. Intraoperative findings included turbid dark brown pericardial fluid and a nipple-shaped protrusion on the external aspect of the noncoronary sinus of Valsalva. Histologically, the lesion was enclosed by intact media and adventitia, and represented an organized hematoma. Dilated venules noted adjacent to the lesion were suggestive of an intramural hemangioma. The etiology of this lesion is unclear, but it might be an unusual type of intramural hematoma (IMH) and gives us a hint of an origin of IMH.