A billiard ball in the left atrium.

An 84-year-old woman with a history of severe systolic heart failure, a mechanical mitral valve, and atrial fibrillation presented to the hospital with syncope and is found to have a free-floating intracardiac mass on transthoracic echocardiogram that was absent 5 months earlier. Real time three-dimensional (3D) transesophageal echocardiography (TEE) images reveal a billiard-ball-looking mass thought to be a large left atrial thrombus causing syncope by transiently obstructing the mitral valve orifice. Real time 3D TEE offers several potential advantages for the evaluation of intracardiac masses.