Thus far, little has been written concerning echocardiographic identification of the oblique vein of the left atrium, or Marshall's vein. There is much discussion, nonetheless, on the potential significance of the vein, or its ligamentous remnant, as an arrhythmic substrate. We describe here four patients in whom transthoracic echocardiography revealed a venous structure protruding within the cavity of the left atrium. We discuss the possibility that these structures represent Marshall's vein, albeit probably as part of a persistent left superior caval vein.