The Collaborative International Dictionary of English v.0.48:

cardiograph \car"di*o*graph\, n. [Gr. kardi`a heart + -graph.]
   (Med.)
   An instrument which, when placed in contact with the chest,
   will register graphically the comparative duration and
   intensity of the heart's movements.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cardiograph
    n 1: medical instrument that records electric currents
         associated with contractions of the heart [syn:
         cardiograph, electrocardiograph]
    2: 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 [syn:
       ballistocardiograph, cardiograph]