ballistocardiograph

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A device used to determine the volume of blood passing through the heart in a specific period of time and the force of cardiac contraction by measuring the body's recoil as blood is ejected from the ventricles with each heartbeat.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An instrument which measures ballistic forces on the heart, 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.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a medical instrument that measures the mechanical force of cardiac contractions and the amount of blood passing through the heart during a specified period by measuring the recoil of the body as blood is pumped from the ventricles