The reason our patient’s heart is pushed to the left is because the pneumothorax is large enough to exert pressure (light blue arrows), a condition called a ‘tension’ pneumothorax. This can have very severe effects on the patient if the pressure is high enough to interfere with the ability of blood to return to the heart. There is also a very flat contour at the bottom of the left lung (dark blue), an air-fluid level. This tells us that there is also some sort of fluid in the pleural space on the left, along with the air. This is most likely blood (red).