Cardiac Cycle & PV Loops
Core valve events, heart sounds, and pressure–volume loop reasoning for preload, afterload and contractility.
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Questions Covered in This Set
10 cards to master
What single rule governs all valve events?
Valves are passive — they open and close only when the pressure gradient across them reverses.
What causes S1?
Mitral (and tricuspid) valve closure when LV pressure rises above LA pressure, marking the start of isovolumetric contraction.
What causes S2, and what appears on the aortic trace?
Aortic (and pulmonic) valve closure when aortic pressure exceeds falling LV pressure; the dicrotic notch appears on the aortic trace.
Typical EDV, ESV, SV and EF values
EDV ≈120 mL, ESV ≈50 mL, SV = EDV − ESV ≈70 mL, EF = SV/EDV ≈58%.
What do the width and area of a PV loop represent?
Width = stroke volume; area = stroke work.
What is the ESPVR and why is E_max the best contractility index?
The end-systolic pressure–volume relationship, a near-linear line touching the top-left corner of every loop; its slope E_max is load-independent, unlike ejection fraction.
What does the EDPVR reflect?
The curved lower boundary of the loop — ventricular compliance (diastolic stiffness).
How does increased preload change the PV loop?
Bottom-right corner slides right along the EDPVR: EDV↑, ESV unchanged, SV↑ (Frank–Starling).
How does increased afterload change the PV loop?
Loop becomes taller and narrower: higher pressure needed to open the aortic valve, ejection stops earlier on the ESPVR, ESV↑ and SV↓.
When are S3 and S4 heard?
S3 during rapid filling into a dilated, volume-overloaded ventricle; S4 with atrial kick into a stiff, hypertrophied ventricle.
