A 72 year old woman was admitted for cardiac surgery because of a symptomatic mitral stenosis. She reported intermittent attacks of dyspnoea, increasing over the previous few months. She had an ischaemic cerebral infarction five years ago without any residual effects, and a thrombembolic occlusion of the right femoral artery one month previously, when anticoagulation with coumarin was started. Because of inadequate image quality by transthoracic examination a transoesophageal echocardiography was performed preoperatively. A highly mobile left atrial thrombus could be seen, floating free during systole (A). Diastolic left ventricular inflow leads to an entrapment of the thrombus within the stenotic mitral valve (B) with intermittent reduction of blood flow, as shown by pulse wave Doppler (C). Immediately after examination the patient developed signs of a lung oedema and was operated on as an emergency. The left atrial thrombus was removed and the mitral valve replaced with a 29 mm mechanical prosthesis. Apart from a transient neurological deficit the postoperative course was uneventful.

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This case underlines the necessity of anticoagulation in rheumatic mitral valve disease and demonstrates the typical appearance of a ball shaped thrombus in the left atrium. Owing to an increasingly widespread use of anticoagulation over recent years comparable complications might be prevented in future.