Cardiac Cycle, JVP & Pressure-Volume Loops

Rapid Review·Cardiovascular

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PHYSIOLOGY

T1Must know

FA P291-292

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Focus on

Four phases bounded by valve events, the venous waveform that reads as a diagnosis, and how each valve lesion deforms the loop.

Key takeaways

Phases of the left ventricle

The rule

each phase is bounded by a valve event. Follow them counter-clockwise around the pressure-volume loop, then see them aligned with the sounds and the ECG on the Wiggers diagram.

What this shows

Left ventricular pressure-volume loop. The loop runs counter-clockwise: mitral valve closes (S1), isovolumetric contraction, aortic valve opens, ejection, aortic valve closes (S2), isovolumetric relaxation, mitral valve opens, filling. Width of the loop is stroke volume (EDV minus ESV). Overlaid: raising contractility narrows ESV and raises SV and EF; raising afterload raises aortic pressure and ESV and lowers SV; raising preload widens the loop to the right and raises SV.

Isovolumetric contraction (systole)

between mitral closure and aortic opening. The period of highest oxygen consumption, because the ventricle generates maximal pressure while doing no external work.

Systolic ejection (systole)

between aortic opening and aortic closure.

Isovolumetric relaxation (diastole)

between aortic closure and mitral opening.

Rapid filling (diastole)

just after mitral opening.

Reduced filling (diastole)

just before mitral closure.

Dicrotic notch

slight ↑ of aortic pressure in the early diastole that corresponds to closure of the aortic valve.

Coronary blood flow

peaks during early diastole.

Which valve event bounds each phase
Phase	Begins with	Ends with
Isovolumetric contraction	Mitral closes (S1)	Aortic opens
Systolic ejection	Aortic opens	Aortic closes (S2)
Isovolumetric relaxation	Aortic closes (S2)	Mitral opens
Rapid filling	Mitral opens	Reduced filling begins

The jugular venous pulse

Reading the waveform

the normal JVP is the reference; all five patterns sit side by side below.

What this shows

Jugular venous pressure tracings compared. Normal shows a, c, v waves with x and y descents. Atrial fibrillation loses the a waves. Tricuspid regurgitation loses the x descent and fuses c and v into a single tall cv wave. Constrictive pericarditis has a sharp prominent y descent. Cardiac tamponade has no y descent at all.

Atrial fibrillation gives absent a waves

because there is no organized atrial contraction to produce one.

Tricuspid regurgitation gives an absent x descent

because the atrium never truly relaxes against a competent valve; c and v fuse into a single tall cv wave.

Constrictive pericarditis gives a prominent y descent

the RA empties fast, then the ventricle hits the rigid pericardium.

Cardiac tamponade gives an absent y descent

because the RV cannot fill at all.

The jugular venous pulse waveform
Wave	Represents	Abnormalities
a wave	Atrial contraction	Prominent (cannon a wave) in AV dissociation and raised RV end-diastolic pressure. Absent in atrial fibrillation
c wave	RV contraction, the closed tricuspid bulging into the atrium
x descent	Atrial relaxation plus downward pull of the closed tricuspid valve	Reduced or absent in tricuspid regurgitation and right heart failure
v wave	Rising RA pressure as it fills against a closed tricuspid valve (venous return)	Tall in tricuspid or mitral regurgitation
y descent	RA emptying into the RV	Prominent in constrictive pericarditis; absent in cardiac tamponade

JVP tracing to diagnosis
Tracing abnormality	Diagnosis
Absent a waves	Atrial fibrillation
Cannon a waves	AV dissociation (third-degree block)
Absent x descent	Tricuspid regurgitation
Prominent y descent	Constrictive pericarditis
Absent y descent	Cardiac tamponade
Tall v wave	Mitral or tricuspid regurgitation

Pressure-volume loops in valvular disease

Aortic stenosis

on the aortic stenosis loop: LV pressure exceeds aortic pressure, ESV rises and SV falls, EDV is unchanged if mild, and hypertrophy lowers compliance so end-diastolic pressure is higher for a given EDV.

Aortic regurgitation

on the aortic regurgitation loop: EDV rises, ESV falls, SV rises, there is no true isovolumetric phase, the pulse pressure is wide, and the dicrotic notch is lost.

Mitral stenosis

on the mitral stenosis loop: LA pressure far exceeds LV pressure through diastole, EDV falls because filling is obstructed, and SV falls with it.

Mitral regurgitation

on the mitral regurgitation loop: LA pressure rises (tall v wave), there is no true isovolumetric phase, ESV falls because blood escapes backward into the low-resistance atrium during systole, and EDV rises as that volume returns.

PV loop changes by lesion
Lesion	EDV	ESV	SV	Isovolumetric phases	Signature
Aortic stenosis	Unchanged if mild	Raised	Reduced	Preserved	LV pressure > aortic pressure; raised EDP for a given EDV
Aortic regurgitation	Raised	Reduced	Raised	Lost	Wide pulse pressure; loss of dicrotic notch
Mitral stenosis	Reduced	Reduced	Reduced	Preserved	LA pressure far above LV in diastole
Mitral regurgitation	Raised	Reduced	Total raised, forward reduced	Lost	Tall v wave

Why the regurgitations have "no true isovolumetric phase"
Lesion	Which valve leaks	Consequence
Aortic regurgitation	Aortic valve never fully closes	Blood enters the LV during "isovolumetric relaxation", so the volume is not constant
Mitral regurgitation	Mitral valve never fully closes	Blood leaves the LV during "isovolumetric contraction", so the volume is not constant

Which phase of the cardiac cycle uses the most oxygen, and why?

Isovolumetric contraction. The ventricle generates maximal pressure while doing no external work.

How it's tested

Isovolumetric contraction is the period of highest myocardial oxygen consumption, because the ventricle generates maximal pressure while performing no external work, and that reasoning is what the question is checking. Every phase boundary is a valve event, so a stem naming a valve opening or closing is really asking which phase begins.

A prominent y descent means constrictive pericarditis and an absent y descent means tamponade. The two look similar at the bedside, so the waveform is what separates them: in constriction the ventricle fills fast and then stops abruptly against the rigid pericardium, while in tamponade it never fills at all. The regurgitant lesions lose their isovolumetric phases for a purely mechanical reason, which is that a leaking valve makes constant volume impossible, and reasoning it out beats memorising the table.

Go deeper

First Aid 2026 — CV/Physiology (p.291-292) · B&B — Cardiac cycle & PV loops; JVP waveforms · Mehlman — HY Cardio (Wiggers, a/c/v waves, constriction vs tamponade)

High-yield images8

Left ventricular pressure-volume loop. The loop runs counter-clockwise: mitral valve closes (S1), isovolumetric contraction, aortic valve opens, ejection, aortic valve closes (S2), isovolumetric relaxation, mitral valve opens, filling. Width of the loop is stroke volume (EDV minus ESV). Overlaid: ra

The Wiggers diagram: aortic, left ventricular and left atrial pressure tracings aligned with heart sounds, ventricular volume, the jugular venous (right atrial) a-c-v waveform, and the ECG across one 0.8 second cycle. It shows which valve event bounds each phase, where the dicrotic notch falls after

Jugular venous pressure tracings compared. Normal shows a, c, v waves with x and y descents. Atrial fibrillation loses the a waves. Tricuspid regurgitation loses the x descent and fuses c and v into a single tall cv wave. Constrictive pericarditis has a sharp prominent y descent. Cardiac tamponade h

Aortic stenosis: pressure-volume loop and pressure tracing. LV pressure exceeds aortic pressure through systole, ESV rises and stroke volume falls, EDV is unchanged if mild, and ventricular hypertrophy lowers compliance so end-diastolic pressure is higher for any given EDV.

Aortic regurgitation: pressure-volume loop and pressure tracing. There is no true isovolumetric phase because the aortic valve never fully closes; EDV and stroke volume both rise, the pulse pressure is wide, and the dicrotic notch is lost.

Mitral stenosis: pressure-volume loop and pressure tracing. Left atrial pressure exceeds LV pressure throughout diastole; impaired filling lowers EDV, and ESV and stroke volume fall with it.

Mitral regurgitation: pressure-volume loop and pressure tracing. There is no true isovolumetric phase because the mitral valve never fully closes; ESV falls as blood escapes backward into the left atrium during systole, the returning volume raises EDV, and a tall v wave appears on the atrial tracing

Cardiac Cycle, JVP & Pressure-Volume Loops

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During which phase of the cardiac cycle is oxygen consumption the highest?

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PreviousResistance, Pressure, Flow & Cardiac/Vascular Function Curves NextHeart Sounds: S1-S4 & Splitting of S2

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