Four phases: isovolumetric contraction, ejection, isovolumetric relaxation, filling. Loop width = stroke volume; loop area = stroke work.
Why this is true
The loop is simply pressure plotted against volume through one beat, bounded by two physiological limits. The end-systolic pressure–volume relationship (ESPVR) is the maximum pressure the ventricle can generate at any volume — its slope *is* contractility, independent of load. The end-diastolic pressure–volume relationship (EDPVR) is passive ventricular compliance. Every haemodynamic intervention moves the loop between these two curves: preload shifts the right-hand corner, afterload shifts where ejection begins, and inotropes rotate the ESPVR itself. Reading a loop is therefore reading which of those three was changed.
Key points
Valve lesion → loop signature
| Lesion | Loop change | Missing phase |
|---|---|---|
| Aortic stenosis | Tall and narrow, high peak pressure | None |
| Aortic regurgitation | Wide, shifted right | Isovolumetric relaxation |
| Mitral regurgitation | Wide, low end-systolic volume | Isovolumetric contraction |
| Mitral stenosis | Small loop, low preload | None |
Common traps
- Ejection fraction looks deceptively normal in mitral regurgitation because the ventricle unloads into the low-pressure atrium.
- Contractility cannot be judged from stroke volume alone — only the ESPVR slope is load-independent.
Clinical case
A patient's PV loop shows no isovolumetric contraction segment and a markedly increased loop width with reduced end-systolic volume.
High-yield
Loss of the isovolumetric contraction segment on the PV loop = mitral regurgitation.