What happens when you have an air embolism?

Nothing usually: The air typically is broken up as it goes through tissues- rare it causes strokes or other issues.

Occasional problems: As dr. Simpson says, usually nothing happens when a small amount of air enters the veins. It is trapped in the lung and absorbed. However, if the amount of air is large, it can block blood flow in the lung. Also, if there is a hole in the heart (atrial septal defect), or a so-called "shunt" of blood that bypasses the lung, air can get into the arteries and cause a stroke.