Myxoma of the left atrium is known to mimic the clinical and hemodynamic features of mitral valvular disease. The tumor was diagnosed by using the Echophonocardiography, CAT-scanning, and hemodynamic studies including left heart catheterization and angiography. The diagnosis was confirmed at operation. An electrocardiographic timing signal permitted correlation of heart sounds and pressure waves with movement of the tumor between the left atrium and the left ventricle. In early systole, the tumor suddenly moved from left ventricle to the left atrium, and a notch in the rising left ventricular pressure, a prominant c-wave, and loud, late element of the first heart sound were noted. In early diastole, the tumor moved rapidly through the mitral valve, causing an abrupt diminution in the left atrial volume, thus-causing rapid y-descent despite severe obstruction of the mitral valve. An early diastolic sound, thought to be an opening snap, appeared to be related to the checking of the tumor in the left ventricle.(Tumor plop). The unusual left atrial pressure pulse permits accurate preoperative diagnosis in left atrial myxoma. In this respect we evaluated the accuracy of the preoperative noninvasive studies for the diagnosis of intra-cardiac myxoma.