The pressure-volume relation in the left ventricle and the pump function of the heart.

The concept of body force (force per unit volume) is introduced to account for the effect of the force generated in the radial direction by the active state of the myocardium in an elastic model of the left ventricle represented as a thick-walled cylinder contracting symmetrically. Experimental evidence for the validity of the model is presented. It is shown how the radial force/unit area developed by the myocardium on its inner surface can be included in the equation of the pressure-volume relation (P-V relation) of the left ventricle according to the Suga-Sagawa model, as well as in the formalism that describes the pump function of the heart.