Instantaneous Force-Velocity-Length Determinants in the Contraction of Heart Muscle

The relations of force and velocity during the course of shortening of heart muscle have been explored using the cat papillary muscle. It has been shown that at any instant during contraction the course of muscle shortening is described by the instantaneous relations of force-velocity and muscle length. The three dimensional force-velocity length diagram allows for greater generalization in the analysis of contraction of heart muscle than has been afforded by the analysis of force and velocity relative to initial muscle length alone, and provides a useful construct for portraying a given contractile state of heart muscle. A change in the velocity coordinate of this diagram (V max ) with or without a change in the force coordinate (P o ) serves to define a change in the contractile state of heart muscle.