This preliminary study demonstrates the superiority of live three-dimensional transthoracic echocardiography (3D TTE) over two-dimensional (2D) TTE in the assessment of left atrial (LA) tumors in four patients studied by us (three myxomas, one hemangioma, all subsequently pathologically proven). Because of the unique ability of live 3D TTE to systematically section and view the contents of an intracardiac mass, LA myxomas in the three patients studied could be more confidently diagnosed by noting isolated echolucent areas consistent with hemorrhage/necrosis in the tumor mass. On the other hand, a definite echolucent area was found by 2D TTE in only two of the three patients with myxoma. In the fourth patient with a hemangioma, live 3D TTE showed much more extensive and closely packed echolucencies with little solid tissue as compared to a myxoma consistent with a highly vascularized tumor. In contrast, 2D TTE demonstrated only two isolated echolucencies in the tumor suggesting an erroneous diagnosis of myxoma.