[Stratos]

Originally Posted by thecarrotdude What happens if you inject air into your vein?

Wikipedia to the rescue.

An air embolism, or more generally gas embolism, is a medical condition caused by gas bubbles in the bloodstream (embolism in a medical context refers to any large moving mass or defect in the blood stream). Small amounts of air often get into the blood circulation accidentally during surgery and other medical procedures, but most of these in veins are stopped at the lungs, and a venous air embolism that shows symptoms are very rare. Death may occur if a large bubble of gas becomes lodged in the heart, stopping blood from flowing from the right ventricle to the lungs (this is similar to vapor lock in engine fuel systems). However, the amount of gas necessary for this to happen is quite variable, and also depends on a number of other factors, such as body position.