graphic recording of the stroke volume of the heart for the purpose of calculating cardiac output. The heartbeat results in motion of the body, which in turn causes movements in a suspended supporting structure, usually a special table or bed on which the subject is lying, and these movements are recorded photographically (ballistocardiogram, or BCG) as a series of waves. The BCG is one of the most sensitive measures of the force of the heartbeat, and an abnormality appearing in the BCG of an apparently healthy subject aged 40, or younger, may be suggestive of symptomatic coronary disease.