Free-floating ball thrombus in the left atrium.

Free-floating ball thrombi in the left atrium are rarely seen. They can cause sudden death by occluding the mitral valve. A 47-year-old female patient who showed signs of mitral stenosis during a physical examination and atrial fibrillation by electrocardiography was not administered anticoagulant therapy. On the transthoracic echocardiogram, a stenotic mitral valve and a floating mobile mass were seen inside the large left atrium. This mass was rounded (ball-like), had smooth contours, and occasionally occluded the stenotic mitral valve. The patient underwent emergency surgery to remove the mass, which was later proven to be a thrombus pathologically. Additionally, mitral valve replacement was performed. The importance of anticoagulant therapy for patients with rheumatic mitral stenosis has been emphasized by this case.