The useful work done by the left ventricle is the generation of pressure and flow within the circulation. While pressure and flow are accessible concepts, the models used to describe the ventricular mechanics that are responsible for pressure and flow are increasingly obscure. In a recent issue of Heart, Popovic and colleagues describe some simple observations about changes in ventricular pressures and volumes before and after the Batista procedure.1 The message is simple but expressed in the language of modern ventricular mechanics, it is difficult to disentangle.

In isolated heart muscle preparations the relations between tension and length, and shortening velocity and length, are well known. Attempts to describe the contractile performance in the intact left ventricle in vivo extrapolate these relations, substituting intracavity pressure for tension and volume change for length change. Indices of contractile function have thus been described from analysis of pressure-time relations (dp/dt max), or dimension-time relations (Vmax). Apart from the technical difficulties associated with actually …