English: Left pneumothorax. This X-ray is used on clinicalcases.org to illustrate a fictional case history of tension pneumothorax. Note the large, well-demarcated area devoid of lung markings, the tracheal deviation and movement of the heart away from the affected side. There is also small pleural effusion on the left side.

The patient's left is your right (as if you are looking at the patient facing you). The left-right orientation is assisted by the shape of the heart, a small amount of air in the stomach under the left side of the diaphragm on the left, and the radio-opaque liver under the right side of the diaphragm. The sternoclavicular joints are symmetrically situated indicating that the X-ray is not rotated. Generally, a radiopaque X-ray marker showing L or R indicates the patient's orientation, but one is not present on this X-ray. The metallic spots are snaps for EKG (or ECG) readings.