SUMMARY A 55-year-bld woman has been hospitalized with a complaint - of frequent syncopal attacks, especially when she lay over her back. She had no overt signs of heart failure and rhythm was atrial fibrillation. Preoperative echocardiographic study revealed a left atrial mass strongly suffestive of myxoma. At the operation, an egg shaped, with smooth surface thrombus was found in the left atrium. There were no any other thrombi, neither atrium nor atrial appandage, and the mitral valve was slightly stenotic.