Medservatory
USMLE Step 1Cardiovascular physiologyEP 01 of 16

Pressure-volume loop explained: four phases, four valve events

One heartbeat drawn as a single shape. Learn which corner of the pressure-volume loop is which valve, which way the loop runs, and how to read stroke volume and ejection fraction straight off it.

  • 5:00 video
  • 3 min read
  • 7 sources
  • Published 23 Oct 2026
Video lesson · 5:00 · Watch on YouTubeSeries: Pressure–Volume Loops & Cardiac Physiology · @medservatory
Chapters (15)
By the end of this lesson

Identify the four phases of the left-ventricular pressure–volume loop and the valve event at each corner, read EDV, ESV and stroke volume from the loop, and compute the ejection fraction.

The short version

  1. The left-ventricular pressure-volume loop plots LV pressure (mm Hg) against LV volume (mL) for one beat, and it runs anticlockwise.
  2. The mitral valve closes at the bottom right corner (EDV, part of S1) and opens at the bottom left; the aortic valve opens at the top right and closes at the top left (ESV, S2).
  3. The two vertical sides are the isovolumetric phases: both valves are shut, so volume cannot change.
  4. The width of the loop is stroke volume (EDV − ESV), stroke volume divided by EDV is ejection fraction, and the area inside the loop is stroke work.

What a pressure-volume loop plots

A pressure-volume loop (PV loop) plots the pressure inside the left ventricle against its volume over one heartbeat. Volume, in millilitres, runs along the x-axis; pressure, in millimetres of mercury, runs up the y-axis. Over one beat the line closes on itself into a loop, and it repeats with every beat.[1][4]

Picture the ventricle as a balloon with two doors. The mitral valve is the way in, from the left atrium. The aortic valve is the way out, into the aorta.[2]

Two rules explain the whole loop. A door opens only when the pressure behind it is higher than the pressure in front of it. And when both doors are shut, the volume cannot change at all.[1][2] Every corner of the loop is a valve opening or closing.

The four corners: valve events on the PV loop

Start at the bottom right corner, the end of filling. The ventricle is at its fullest, about 120 mL, at a low pressure of roughly 8–12 mm Hg. That volume is the end-diastolic volume (EDV).[2][3]

The four corners of the left-ventricular PV loop (teaching values)
CornerValve eventWhen it happensMarks
Bottom rightMitral valve closesContraction starts and LV pressure rises above left atrial pressureEDV ≈ 120 mL; part of S1
Top rightAortic valve opensLV pressure passes aortic diastolic pressure, ≈ 80 mm HgStart of ejection
Top leftAortic valve closesLV pressure has fallen far enough at the end of ejectionESV ≈ 50 mL; S2
Bottom leftMitral valve opensLV pressure falls below left atrial pressureStart of filling

So the mitral valve owns the two bottom corners and the aortic valve owns the two top corners. Mitral closure is part of the first heart sound; aortic closure is the aortic (A2) part of the second heart sound.[4][2]

Each corner is a hand-over between phases. At the bottom right, filling ends and isovolumetric contraction begins. At the top right, ejection begins. At the top left, ejection ends and isovolumetric relaxation begins. At the bottom left, filling begins again.

The four phases of the pressure-volume loop

Between the corners lie the four phases of the cardiac cycle: isovolumetric contraction, ejection, isovolumetric relaxation and filling.[1][5]

  1. Phase 1: isovolumetric contraction (right side)Both valves are shut, so pressure shoots up while volume stays put. That is a vertical line at the EDV. It ends when the aortic valve opens, at about 80 mm Hg.[1][4]
  2. Phase 2: ejection (top)Blood leaves, so volume falls and the line travels left. Pressure climbs to a peak of about 120 mm Hg, then eases down as the muscle begins to relax. It ends when the aortic valve snaps shut.[1][4]
  3. Phase 3: isovolumetric relaxation (left side)Both valves are shut again, so pressure drops straight down at a constant volume, the end-systolic volume (ESV), about 50 mL. It ends when the mitral valve opens.[1][2]
  4. Phase 4: filling (bottom)The mitral valve is open and volume grows along the bottom, back to the start, while pressure stays low.[1]

Which way the loop runs

Traced in that order, the loop runs anticlockwise: along the bottom (filling), up the right side (isovolumetric contraction), across the top from right to left (ejection), and down the left side (isovolumetric relaxation).[5]

Reading stroke volume, ejection fraction and stroke work

First, find EDV and ESV from the valve events. The mitral valve closes at the end of filling, so the volume at mitral closure is the EDV. The aortic valve closes at the end of ejection, so the volume at aortic closure is the ESV. On the loop, they are read on the volume axis, under the right and left vertical sides.[1][2]

The width of the loop, end-diastolic minus end-systolic volume, is the stroke volume.[1][5]

Stroke volume and ejection fraction
SV = EDV − ESV EF = SV / EDV

EF uses EDV alone as the denominator.[3]

Worked example: the teaching loop
  1. EDV ≈ 120 mL, ESV ≈ 50 mL
  2. SV = 120 − 50 = 70 mL
  3. EF = 70 / 120 ≈ 0.58 → about 58%

The area inside the loop is the stroke work of that beat.[1][5]

Practice question

Original · USMLE style
Your turnQB-MS-S1-CARD-001-01

A 22-year-old man volunteers for a cardiovascular physiology study. He has no medical history and takes no medications. Pulse is 64/min and blood pressure is 120/80 mm Hg. A conductance catheter records his left ventricular pressure–volume loop at rest. On the loop, the mitral valve closes at a left ventricular volume of 140 mL, and the aortic valve closes at a left ventricular volume of 60 mL.

Which of the following is closest to this patient's left ventricular ejection fraction?
Pick one option. Your answers stay on this device.

Common questions

Which way does a pressure-volume loop run?

With volume on the x-axis and pressure on the y-axis, the left-ventricular loop runs anticlockwise: filling along the bottom, isovolumetric contraction up the right side, ejection across the top and isovolumetric relaxation down the left side.

Where does the mitral valve close on a PV loop?

At the bottom right corner, the end of filling. That point marks the end-diastolic volume, and mitral closure is part of the first heart sound.

Why are two sides of the PV loop vertical?

They are the isovolumetric phases. Both valves are shut, so pressure changes while volume cannot.

What does the width of the pressure-volume loop represent?

The width, EDV minus ESV, is the stroke volume. With EDV 120 mL and ESV 50 mL, that is 70 mL.

What does the area inside the PV loop represent?

The area inside the loop is the stroke work of that beat.

Transcript

Read the full narration, by chapter673 words

0:00One heartbeat as a loop

One heartbeat, drawn as a single shape. Plot the pressure inside the left ventricle against its volume for one beat, and the line closes on itself into a loop. Every corner of that loop is a valve opening or closing. So which way does the loop run, and which corner is which? By the end of this lesson, you'll name the four phases, place each valve event, and read stroke volume and ejection fraction off the loop.

0:27The axes: LV volume and LV pressure

First, the axes. The volume of the left ventricle, in millilitres, runs along the bottom. The pressure inside it, in millimetres of mercury, runs up the side.

0:39Two doors: mitral in, aortic out

Now picture the ventricle as a balloon with two doors. The mitral valve is the way in, from the left atrium. The aortic valve is the way out, into the aorta. A door opens only when the pressure behind it is higher than the pressure in front of it. And when both doors are shut, the volume can't change at all.

1:00End-diastole: mitral closes (S1)

Let's start at the bottom right corner: the end of filling. The ventricle is at its fullest, about 120 mL, at a low pressure of roughly 8 to 12 mm Hg. That volume is the end-diastolic volume, EDV. Contraction starts, ventricular pressure rises above atrial pressure, and the mitral valve closes, part of the first heart sound.

1:26Phase 1: isovolumetric contraction, then the aortic valve opens

Phase 1: isovolumetric contraction. Both valves are shut, so pressure shoots up while volume stays put. That's a vertical line. When ventricular pressure passes the diastolic pressure in the aorta, about 80, the aortic valve opens. That's the top right corner.

1:46Phase 2: ejection

Phase 2: ejection. Blood leaves, so volume falls, and the line travels left. Pressure climbs to a peak of about 120, then eases down as the muscle begins to relax.

2:00Aortic valve closes (S2) and ESV

When it has fallen far enough, the aortic valve snaps shut. That's the top left corner, and the second heart sound. The blood left behind is the end-systolic volume, ESV, about 50 mL.

2:14Phase 3: isovolumetric relaxation

Phase 3: isovolumetric relaxation. Both valves are shut again, so pressure drops straight down at a constant volume.

2:24Mitral valve opens · Phase 4: filling

When ventricular pressure falls below left atrial pressure, the mitral valve opens. That's the bottom left corner. Phase 4: filling. Volume grows along the bottom, back to the start, while pressure stays low.

2:40The trap: it runs anticlockwise

Here's the trap. Traced in that order, the loop runs anticlockwise: along the bottom, up the right side, across the top, and down the left side.

2:51Read the loop: SV, EF, stroke work

Now read it. The width of the loop, end-diastolic minus end-systolic volume, is the stroke volume. 120 minus 50 gives 70 mL. Ejection fraction is stroke volume divided by end-diastolic volume. 70 over 120 is about 58%. And the area inside the loop is the stroke work of that beat.

3:17Practice question

Your turn. Pause if you want to work it out. A 22-year-old man in a research study has his left ventricular pressure–volume loop recorded at rest. His mitral valve closes at a volume of 140 mL, and his aortic valve closes at 60 mL. Which value is closest to his ejection fraction?

3:39Answer and explanation

The answer is C: about 57%. The mitral valve closes at the end of filling, so 140 is the end-diastolic volume. The aortic valve closes at the end of ejection, so 60 is the end-systolic volume. Stroke volume is 80, and 80 over 140 is about 57%. B, 43%, divides end-systolic volume by end-diastolic volume. That's the fraction left behind, not the fraction ejected. A divides the stroke volume by both volumes added together, and D divides the leftover volume by the stroke volume. And E, 80, is the stroke volume in mL, not a percentage.

4:26Recap

Quick recap. One: the loop runs anticlockwise, and the mitral valve closes bottom right and opens bottom left. Two: the aortic valve opens top right and closes top left, and the vertical sides are the isovolumetric phases. Three: the width is stroke volume, stroke volume over EDV is ejection fraction, and the area is stroke work.

4:52Next: preload

Next: what happens to this loop when we fill the ventricle with more blood? That's preload.

Sources

Numbers in the text, e.g. [1], point here
  1. Klabunde RE. Ventricular Pressure-Volume Relationship. Cardiovascular Physiology Concepts (cvphysiology.com, rev. 2023). cvphysiology.com/cardiac-function/cf024
  2. Klabunde RE. Cardiac Cycle. Cardiovascular Physiology Concepts (cvphysiology.com). cvphysiology.com/heart-disease/hd002 · cvphysiology.com/heart-disease/hd002a
  3. Klabunde RE. Cardiac Inotropy; Ventricular Ejection Fraction. Cardiovascular Physiology Concepts (cvphysiology.com). cvphysiology.com/cardiac-function/cf010 · cvphysiology.com/cardiac-function/cf012
  4. Pollock JD, Makaryus AN. Physiology, Cardiac Cycle. StatPearls (updated 3 Oct 2022). ncbi.nlm.nih.gov/books/NBK459327/
  5. Bastos MB, Burkhoff D, et al. Invasive left ventricle pressure–volume analysis: overview and practical clinical implications. Eur Heart J. 2020;41(12):1286–1297. doi:10.1093/eurheartj/ehz552 pmc.ncbi.nlm.nih.gov/articles/PMC7084193/
  6. Burkhoff D, Mirsky I, Suga H. Assessment of systolic and diastolic ventricular properties via pressure-volume analysis. Am J Physiol Heart Circ Physiol. 2005;289(2). journals.physiology.org/doi/full/10.1152/ajpheart.00138.2005
  7. O'Keefe E, Singh P. Physiology, Cardiac Preload. StatPearls. ncbi.nlm.nih.gov/books/NBK541109/

Typical values vary with body size, sex and conditioning. The loop on screen is a teaching model with illustrative values: EDV ≈ 120 mL, ESV ≈ 50 mL, peak ≈ 120 mm Hg, aortic opening ≈ 80 mm Hg.

The practice question is original and its patient is synthetic. Every fact is checked against the sources above in independent accuracy reviews. Always follow your local guidelines and your own laboratory’s ranges.

Image credits. Illustrations: Servier Medical Art (smart.servier.com), CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/), adapted (cropped, recoloured, outlined): heart frontal section. Cardiac cycle illustrations ("cardiac-cycle-1", "cardiac-cycle-3") by Servier via Bioicons (bioicons.com), CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/), adapted (cropped, recoloured, outlined). 3D heart: "Anatomical Human Heart" by Nexal 3D (BlenderKit). The pressure–volume loop, the schematic ventricle and all handwriting are drawn in code (original).

Corrections. None so far. Spotted an error? Email info@medservatory.com with the lesson code MS-S1-CARD-001.

For exam study only, not medical advice. Read the medical disclaimer.

In this series

Playlist on YouTube
  1. EP 01Pressure-volume loop explained: four phases, four valve events5:00
  2. EP 02Preload on the pressure-volume loop: EDV, stroke volume and the EDPVR5:04
  3. EP 03Afterload on the pressure-volume loop4:49
  4. EP 04Contractility on the pressure-volume loop: the ESPVR explained5:17
  5. EP 05Wiggers diagram explained: the cardiac cycle step by step5:30
  6. EP 06The Frank-Starling curve: preload, inotropy and heart failure4:44
  7. EP 07Aortic stenosis vs mitral regurgitation on the pressure-volume loop5:41
  8. EP 08Fick principle: how to calculate cardiac output5:07
  9. EP 09HFrEF vs HFpEF on the pressure-volume loop5:33
  10. EP 10Poiseuille's law and vascular resistance: why arterioles matter5:15
  11. EP 11Venous return and cardiac function curves: where they cross5:11
  12. EP 12The baroreceptor reflex: from stretch to vagal and sympathetic output5:17
  13. EP 13Myocardial oxygen supply and demand: why tachycardia causes ischaemia4:50
  14. EP 14Unstable angina vs NSTEMI vs STEMI: from plaque to ACS4:50
  15. EP 15Antianginal drugs: nitrates, beta blockers, calcium channel blockers4:56
  16. EP 16Complications of myocardial infarction, by timeline4:59