Left atrial ball thrombus is a rare disorder with potential fatal systemic embolism or mitral valve orifice occlusion that may result in sudden death. Its treatment is still controversial and is often associated with poor prognosis. We report the case of a 95-year-old woman with a history of permanent atrial fibrillation who was admitted to our hospital for syncope. A two-dimensional echocardiogram showed an enormous left atrial thrombus protruding through the mitral valve orifice. Cardiac surgeons declined to operate on the patient because of her very advanced age. Therefore, she was put on heparin but unfortunately died on day 17, secondary to a sudden cardiovascular arrest.