We report a case of left atrial myxoma simulating a thrombus on transthoracic echocardiography, but correctly diagnosed using transesophageal echocardiography. As this tumor is usually fatal unless surgically resected, a correct diagnosis is essential. Myxomas which do not prolapse between the mitral valve leaflets and coexist with mitral stenosis may be difficult to diagnose accurately using transthoracic echocardiography. The advantages of transesophageal compared with transthoracic echocardiography in the diagnosis of nonclassical left atrial myxoma are discussed.