We report on a male patient suffering from loss of weight, fatigue, fever, eosinophilia, and hyperthyreoidism. The echocardiogram revealed a left atrial mass originating from the posterior mitral leaflet. In combination with the constitutional symptoms a left atrial myxoma was diagnosed. The tumor was surgically removed. Postoperatively therapy with corticosteroids and thiamazole was stopped. During follow-up, eosinophilia and hyperthyreodism could no longer be detected.