Fig 1. Example of PV loop and its interpretation.

Cardiac bioenergetics (left): internal work (I_w) associated with the potential energy or the energetic expenditure necessary to reach optimal conditions for ejection; external work (E_w) associated with the energetic expenditure of the ejection; cardiac efficiency (CE) defined as the ratio $\text{CE}=\frac{{\mathrm{E}}_w}{{\mathrm{E}}_w+{\mathrm{I}}_w}$. Ventricular-arterial coupling (right): ventricular elastance E_es (slope of the end-systolic pressure-volume relationship, ESPVR, at end-systolic pressure-volume point); arterial elastance ${\mathrm{E}}_a=\frac{\text{ESP}}{\text{SV}}$ with ESP being end-systolic pressure and SV = EDV − ESV the stroke volume (subtraction of end-diastolic and end-systolic volumes).