A long mobile structure in the left atrium was detected on transthoracic echocardiography (TTE), prompting a transesophageal echocardiography (TEE). The videos show TEE 2D recordings on the left and 3D on the right, visualizing the thromboembolism-in-transit across the atrial septum. View Video 1 at http://movie-usa.glencoesoftware.com/video/10.1530/ERP-17-0043/video-1.