Ballistocardiography (BCG) is the measure of the ballistic forces of ejection of blood from the heart on the body. Ballistocardiography is a technique for producing a graphical representation of repetitive motions of the human body arising from the sudden ejection of blood into the great vessels with each heart beat. It is a vital sign in the 1-20 Hz frequency range which is caused by the mechanical movement of the heart and can be recorded by noninvasive methods from the surface of the body. (Definition modified from Wikipedia)