A pressure-volume (PV) loop for the left ventricle is generated as left ventricular pressure is plotted against left ventricular volume at multiple time points during a complete cardiac cycle. The cycle can be divided into several basic phases: ventricular filling (diastole), isovolumetric contraction, ejection phase (the top of the curve), and isovolumetric relaxation. The end-diastolic volume in the graph represents diastole at the end of ventricular filling. As the ventricle begins to contract isovolumetrically, the LV pressure increases but the volume remains the same, therefore resulting in a vertical line (all valves are closed). Once LV pressure exceeds aortic diastolic pressure, the aortic valve opens, and ejection begins. During this phase, the LV volume decreases as LV pressure increases to peak systolic pressure and then decreases as the ventricle begins to relax. When the aortic valve closes, ejection ceases and the ventricle relaxes isovolumetrically – the LV volume remains unchanged; therefore the line is vertical (all valves are closed). The LV volume at this time is the end-systolic (i.e., residual) volume. When the LV pressure falls below left atrial pressure, the mitral valve opens and the ventricle begins to fill. The LV pressure falls as the ventricle fills because the ventricle is initially relaxing. Once the ventricle is fully relaxed, however, the LV pressure gradually increases as the LV volume increases. The width of the loop represents the difference between end diastolic volume and end systolic volume which defines the stroke volume. The area within the loop is the ventricular stroke work.
“Cardiac Pressure Volume Loop” by Bitzblitz – Own work. Licensed under CC BY-SA 3.0 via Wikimedia