3DE assessment of cor triatriatum by TTE. (A, B) 3D volume rendering of the left atrium and LV demonstrating location of the membrane in long axis view. (C, D) En-face view of the membrane in the left atrium with residual orifice allowing for communication between upper and lower parts of the left atrium, displayed from two different perspectives. (E) Flexi-slice function allowing for direct 3D quantification of the orifice size. (F) 3D Colour data acquisition demonstrating blood flow through the orifice in the left atrium membrane, hence ensuring that this is a true orifice and not a drop-out artefact.