A case of round left atria1 (LA) thrombus, simulating LA myxoma, is demonstrated by echocardiography, followed by dislodgement of the thrombus 22 hours later to the right leg. After a Fogarty catheter procedure, no traces of atria1 mass could be seen on repeated echocardiograms. Histologic examination confirmed the diagnosis of thrombus. To the best of our knowledge, this is the first case report of a left atria1 thrombus detected by echocardiogram, and dislodged completely. A 73-year-old woman was admitted to the hospital because of palpitations and weakness, which started 3 days preceding admission. Her past medical history was noncontributory. The physical examination was normal, apart from an irregular pulse. Her blood pressure was 110/75 mm Hg. Cardiac examination was normal; no murmurs or clicks were heard. No neurologic deficit was noticed. An ECG demonstrated slow atria1 fibrillation with ventricular response of 80 to 90 bpm and minor anterior wall ST-T changes. Chest roentgenogram was normal, as were routine blood laboratory examinations, including thyroid function tests. Routine echocardiographic examination was normal, except for a floating mass 1 x 2 cm in the normal left atrium, that was attached to the intra-atria1 septum by a short pedicle (Fig. 1). The diagnosis of a left atria1 mass (thrombus or tumor) was made, and the patient was therefore prepared for surgery. Twenty-two hours later, the patient complained of sudden, severe pain in her right leg. The color was white below the knee, and the leg was cold and pulseless. Doppler examination confirmed the disappearance of pulses below the femoral artery. A Fogarty catheter was inserted through an incision in the upper thigh, and a thrombus, measuring 2 X 2 cm, was removed from the popliteal artery. On repeated echocardiograms, no mass could be visualized in the left atrium (Fig. 2). Histologic examination confirmed the diagnosis of a thrombus. The patient was treated with heparin and warfarin sodium, and was discharged in a good, clinical condition 2 weeks later, LA thrombus is found especially in patients with mitral stenosis with enlarged left atrium, in patients after mitral valve replacement, in low cardiac output states, and in patients with atria1 arrhythmias.‘~” Systemic embolization