"The reverse figure 3 sign (also known as the E sign) is seen on barium swallows in patients with coarctation of the aorta and is the medial equivalent of the figure 3 sign seen on plain chest radiographs. It is formed by prestenotic dilatation of the ascending aorta, indentation of the coarctation site (or "tuck"), and post-stenotic dilatation of the descending aorta."