Does the history of contraction affect the pressure-volume relationship?

A comparison is made between two descriptions of the hemodynamic properties of the heart: the ventricular pressure-volume (P-V) relationship, modeled by a time-varying elastance, and the ventricular pump function graph, i.e., the relationship between mean ventricular pressure and output. It appears that, although both descriptions seem to reflect the same myocardial properties, an unexplained discrepancy exists between the assumed linear nature of the time-varying elastance and the curvature of the pump function graph. It is argued that this discrepancy may reflect deviations from the ideal time-varying elastance behavior, such as those observed in isolated cardiac muscle, where the history of contraction affected the P-V relationship.