Fig. 1.

Left panel: A stylized representation of the relation between left ventricular (LV) pressure (Plv) or arterial pressure (Pa) and both the LV pressure-volume relations during a cardiac cycle and arterial elastance (Ea) (red line) along with the associated formulae defining end-systolic elastance (Ees) (blue line) and Ea. Stroke work (SW) is the area within the LV pressure-volume loop for one cardiac cycle, while the potential energy (PE) is the area sub served by the Ea and LV end-systolic volume (ESV). LV efficiency (LVef) is the ratio of SW to SW + PE. Right panel: A stylized representation of the relation between steady-state cardiac output (CO) or venous return (VR) and right atrial pressure (Pra) from the perspective of venous return (blue line) and left ventricular output (red line) illustrating global cardiac efficiency (Eh). The zero CO pressure intercept defines mean systemic pressure (Pms). See text for further discussion