 Background and aims of the study In a normally aerated lung, the only detectable structure is the pleura, visualized as a hyperechoic horizontal line. The pleural line moves synchronously with respiration: this dynamic horizontal movement is called lung sliding 1 representing movement of the two pleural layers as lungs expand during the respiratory cycle 2. Using B-mode, lung sliding appears as a pleural line oscillation from side to side which corresponds to the variation of the underlying artifacts. When M-mode is applied to the lung exam, the system displays a representation of tissue motion over time: in the case of normal lung sliding, the area on the M-mode tracing deep to the pleural line takes on a granular or sandy appearance while the relatively immobile superficial tissues appear smooth and linear. This has been termed Seashore Sign, as the superficial tissues resemble waves and the deeper tissues the sandy beach 2, 3. 