PRIMARY tumors of the heart are rare, slightly more than 300 cases having been reported in the literature. Intra-atrial myxoma is the commonest, constituting approximately 50% of all cases reported. Of these, 75% are said to occur in the left atrium. This tumor has varied clinical manifestations. It is one of the lesions that may simulate mitral valvular stenosis.* Recent advances in the technique for cardiac operation make successful therapy theoretically possible. Therefore, today the early clinical recognition of such tumors is of great practical significance. In five cases recorded before 1954, the clinical diagnosis was made prior to death.† In three of these angiocardiography revealed a constant filling defect of the left atrium ‡ and a surgical exploration was performed. In two an attempt at removal of the tumor was unsuccessful and both patients died. The fourth case was accidentally found in a patient surgically explored for mitral commissurotomy.