There are various devices which the radiologist must be able to identify in the intensive care setting. The intra-aortic balloon pump is one of these. When the balloon inflates it will displace blood in the segment of the aorta it comes to occupy both proximally and distally. The balloon is set to dilate during early diastole (immediately after the aortic valve closes) because this is when the maximum amount of blood is available for displacement.  It is important that the balloon is not malpositioned as when it inflates this could cut off circulation to key areas. Therefore the proximal balloon tip must be distal to the take-off of the left subclavian artery and the distal balloon must be proximal to the take-off of the renal arteries. On plain film, if the radio-opaque tip is seen overlying the AP window the balloon is assumed to be correctly positioned. If it does not lie in this window, you should raise the possibility of malpositioning.