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Human Physiology · Cardiovascular system

The Heart as a Pump: the Cardiac Cycle

Each heartbeat is a sequence of pressure changes that open and close four valves in a fixed order. Learn that sequence once and heart sounds, ejection fraction and the exercise response of a cardiac patient all follow from it.

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Part 3 · Cardiovascular System · Chapter 10 of 47

Learning objectives

By the end of this page you should be able to:

  • Trace blood through the two pumps of the heart and name the valve at each step.
  • Describe the phases of the cardiac cycle and when each valve opens and closes.
  • Read a Wiggers diagram and a pressure–volume loop.
  • Define end-diastolic volume, end-systolic volume, stroke volume and ejection fraction, with typical values.
  • Explain the heart sounds and the effect of heart rate on the length of diastole.
  • Link these ideas to heart failure, valve disease and cardiac rehabilitation.

Why it matters

Physiotherapists work with heart patients on wards, in intensive care and in cardiac rehabilitation. Their notes speak of ejection fraction, murmurs and diastolic dysfunction. Their exercise tolerance depends on how much blood each beat can deliver.

The cardiac cycle is the framework that makes those terms meaningful. It explains why a patient with a stiff ventricle becomes breathless at high heart rates, and why a weak ventricle limits exercise.

Two pumps in series

The heart is two pumps side by side. The right heart receives blood from the body and pumps it through the lungs at low pressure. The left heart receives it from the lungs and pumps it round the body at high pressure. The structure of the chambers and valves is described in Heart and Mediastinum (Human Anatomy).

Figure 1 · Two pumps in series

The path of blood through the right and left heart, lungs and body Blood returns from the body to the right atrium, passes the tricuspid valve into the right ventricle and the pulmonary valve to the lungs. It returns to the left atrium, passes the mitral valve into the left ventricle and the aortic valve to the body. Body tissuesRight atriumRight ventricleLungsLeft atriumLeft ventricleAorta → bodyvenae cavaetricuspidpulmonary valvemitralaortic valveRIGHT HEART — low pressure, to the lungsLEFT HEART — high pressure, to the bodyTwo pumps in series: whatever the right side pumps, the left side must also pump.
The valves make flow one-way. The anatomy of the chambers and valves is in the Human Anatomy page on the heart.

Because the two pumps are in series, over any length of time they must pump the same volume. If the left side falls behind, blood backs up into the lungs. That is the basis of breathlessness in left heart failure.

The phases of the cardiac cycle

The physiologist Carl Wiggers drew the electrical and mechanical events of one beat on a single time axis. His diagram remains the standard way to teach the cycle [1]. Mitchell and Wang argue that students should learn to read it as a set of causes, not memorise it as a picture [1].

Figure 2 · The cardiac cycle (Wiggers diagram)

Pressures, left ventricular volume and heart sounds through one cardiac cycle Pressure traces for aorta, left ventricle and left atrium, a left ventricular volume trace and heart sound marks, across one 0.8 second beat. Shaded phases show atrial systole, isovolumetric contraction, ejection, isovolumetric relaxation and filling. The first heart sound marks mitral closure at the start of contraction, the second marks aortic closure at the end of ejection. Atrial systoleIVCEjectionIVRFilling04080120Aortic pressureLV pressureLA pressuremmHg50120LV volume (mL)S1S2SoundsTime over one beat (about 0.8 s at 75 beats per minute)
Read it top to bottom at any moment. Valves open and close where the pressure lines cross. IVC and IVR: isovolumetric contraction and relaxation. Schematic curves [1].
PhaseValvesWhat happens
Atrial systoleMitral open, aortic closedAtria contract and top up ventricular filling; ends at end-diastolic volume
Isovolumetric contractionAll closedVentricle contracts; pressure rises steeply with no change in volume
EjectionAortic open, mitral closedVentricular pressure exceeds aortic pressure; blood is ejected
Isovolumetric relaxationAll closedVentricle relaxes; pressure falls with no change in volume
Ventricular fillingMitral open, aortic closedRapid passive filling, then slow filling, then the next atrial contraction

The rule that ties it together is simple: a valve opens when the pressure behind it exceeds the pressure in front of it, and closes when that reverses. Every event in the cycle is a crossing of two pressure lines.

Pressures and volumes

MeasureTypical resting adult value
Left ventricular pressureabout 120 mmHg in systole, about 5–10 mmHg at end-diastole
Aortic pressureabout 120/80 mmHg
Right ventricular pressureabout 25 mmHg in systole, a few mmHg at end-diastole
Pulmonary artery pressureabout 25/10 mmHg
End-diastolic volume (EDV)about 120 mL
End-systolic volume (ESV)about 50 mL
Stroke volume (EDV − ESV)about 70 mL
Ejection fraction (SV ÷ EDV)about 52–72% in men, 54–74% in women [2]

These are typical values for a resting adult. The 2015 echocardiography recommendations give the normal ejection fraction range as about 52–72% in men and 54–74% in women [2]. Values below these suggest reduced systolic function.

The pressure–volume loop

Plotting ventricular pressure against volume turns each beat into a loop that is easier to reason with.

Figure 3 · The pressure–volume loop

Left ventricular pressure-volume loop for one heartbeat A loop plotting left ventricular pressure against volume. Filling runs along the bottom from about 50 to 120 millilitres at low pressure; isovolumetric contraction rises vertically at 120; ejection curves across the top back to 50; isovolumetric relaxation falls vertically to the start. The width of the loop is the stroke volume. 1 Filling2 Isovolumetric contraction3 Ejection4 Isovolumetric relaxationESV about 50 mLEDV about 120 mLstroke volume about 70 mLLeft ventricular volume (mL)LV pressure (mmHg)04080120
One beat as a shape. The loop’s width is stroke volume; its area is the work done by the ventricle in one beat. Typical resting values for an adult; schematic.

The loop shows the four phases as its four sides. A weaker ventricle produces a loop shifted to the right, with a larger end-systolic volume and a smaller width. A stiff ventricle that fills poorly produces a steeper bottom edge, because pressure rises quickly as it fills.

Heart sounds

SoundCauseTiming
S1 (“lub”)Closure of the mitral and tricuspid valvesStart of ventricular systole
S2 (“dub”)Closure of the aortic and pulmonary valvesEnd of ejection
S3Rapid filling into a compliant or overloaded ventricleEarly diastole; normal in children and athletes, abnormal in heart failure in older adults
S4Atrial contraction into a stiff ventricleLate diastole; usually abnormal
MurmurTurbulent flow through a narrowed or leaking valve or defectSystolic or diastolic, depending on the lesion

Heart rate and the length of diastole

Figure 4 · Faster heart, shorter filling

Duration of systole and diastole at increasing heart rates Three horizontal bars for heart rates of 75, 120 and 180 beats per minute. Systole shortens only slightly, while diastole shrinks greatly as heart rate rises. 75 beats/minsystolediastole120 beats/minsystolediastole180 beats/minsystolediastoleApproximate durations. As heart rate rises, diastole shortens much more than systole.
Diastole is the time to fill and to perfuse the heart muscle. Very high heart rates squeeze both, which matters in patients with coronary disease. Approximate values.

At 75 beats per minute one cycle lasts 0.8 seconds, with diastole taking about two thirds. As heart rate rises, diastole shortens far more than systole. The left ventricle receives most of its own blood supply during diastole, so very high heart rates reduce both filling time and coronary perfusion.

This is why a patient with angina, aortic stenosis or a stiff ventricle may tolerate a moderate heart rate well but deteriorate quickly at a high one.

Clinical relevance for the physiotherapist

  • Heart failure with reduced ejection fraction. The ventricle empties poorly; stroke volume is limited and rises little with exercise.
  • Heart failure with preserved ejection fraction. Ejection fraction is normal but the stiff ventricle fills poorly, especially at high heart rates.
  • Exercise-based cardiac rehabilitation. A Cochrane review of 44 trials in heart failure found that exercise probably reduces all-cause hospital admissions and may improve quality of life in the short term, with little difference in short-term mortality [3].
  • Valve disease. Aortic stenosis limits the rise in output with exercise and can cause dizziness or fainting on exertion; screen symptoms before exercise.
  • Atrial fibrillation. Loss of atrial contraction removes the final top-up of filling, which matters most when the ventricle is stiff.

Assessment and application

InformationWhere to find itWhy it matters
Ejection fractionEchocardiogram reportIndicates systolic function [2]; informs exercise intensity and monitoring
Murmurs and valve diseaseMedical notes, echocardiogramSome lesions limit safe exercise intensity
Heart rate and rhythmPulse, ECG, monitorHigh rates shorten filling; irregular rhythm reduces efficiency
Symptoms on exertionPatient reportChest pain, dizziness or disproportionate breathlessness are stop signals

Practical skill · reading an echocardiogram report

Find the left ventricular ejection fraction, the description of wall motion, any valve stenosis or regurgitation, and any comment on diastolic function. Write these at the top of your assessment, because they shape how hard and how fast you progress exercise.

Common mistakes

  • Saying the valves open because of muscle action. They open and close passively, by pressure differences.
  • Confusing stroke volume with ejection fraction. One is a volume, the other a proportion.
  • Assuming a normal ejection fraction means a normal heart. Filling can be impaired with a normal ejection fraction.
  • Forgetting that diastole shortens most as heart rate rises.
  • Attributing S1 to the aortic valve. S1 is atrioventricular valve closure.

Exam preparation

Long answer

Describe the events of the cardiac cycle with a labelled diagram. Add a note on heart sounds.

  • Draw the Wiggers diagram: aortic, LV and LA pressures, LV volume, heart sounds (Figure 2) [1].
  • Describe each phase with valve positions (table).
  • Pressures and volumes; stroke volume and ejection fraction [2].
  • Heart sounds with timing.
  • Effect of heart rate on diastole (Figure 4).

Short notes

  • Pressure–volume loop (Figure 3).
  • Ejection fraction and its normal range [2].
  • Third and fourth heart sounds.
  • Exercise-based rehabilitation in heart failure [3].

Viva and practical

  • “When does the aortic valve open?” — when LV pressure exceeds aortic pressure [1].
  • “What is a normal ejection fraction?” — about 52–72% in men and 54–74% in women [2].
  • “Does cardiac rehabilitation help in heart failure?” — it probably reduces hospital admissions in the short term [3].
  • Practical: auscultate S1 and S2 at the apex and base, timing them against the carotid pulse.

Current evidence

Exam and traditional teaching

The Wiggers diagram is memorised as a fixed picture, and heart failure is often taught as a single condition of low ejection fraction.

What the evidence adds

Teaching research recommends using the diagram to reason about cause and effect, including exercise and abnormal beats [1].

Normal ranges for ejection fraction are now sex-specific [2]. Exercise-based rehabilitation benefits people with heart failure, though most trials studied reduced ejection fraction and fewer included older people, women or preserved ejection fraction [3].

What the student should understand

Understand the cycle well enough to predict what changes when a valve narrows, a ventricle stiffens or the heart rate climbs. That is what you will need on the ward.

Check yourself

10 questions on this page. Tap one to see the answer and the reasoning.

Q1. The first heart sound (S1) is caused mainly by:
  1. (A) Closure of the aortic and pulmonary valves
  2. (B) Closure of the mitral and tricuspid valves
  3. (C) Rapid ventricular filling
  4. (D) Atrial contraction

Answer: (B) S1 marks closure of the atrioventricular valves as ventricular pressure rises, a timing the Wiggers diagram makes visible [1].

Q2. During isovolumetric contraction:
  1. (A) Blood is ejected into the aorta
  2. (B) All four valves are closed and pressure rises steeply
  3. (C) The ventricle fills
  4. (D) The atria contract

Answer: (B) Pressure rises with no change in volume until it exceeds aortic pressure [1].

Q3. The aortic valve opens when:
  1. (A) Left atrial pressure exceeds ventricular pressure
  2. (B) Left ventricular pressure exceeds aortic pressure
  3. (C) The ventricle relaxes
  4. (D) The mitral valve opens

Answer: (B) Valves open and close where the pressure traces cross [1].

Q4. With an end-diastolic volume of 120 mL and an end-systolic volume of 50 mL, the ejection fraction is about:
  1. (A) 42%
  2. (B) 58%
  3. (C) 70%
  4. (D) 120%

Answer: (B) Stroke volume 70 ÷ 120 ≈ 58%, within the normal echocardiographic range [2].

Q5. According to the 2015 echocardiography recommendations, the normal range of LV ejection fraction in adult men is about:
  1. (A) 25–40%
  2. (B) 52–72%
  3. (C) 80–95%
  4. (D) Exactly 50%

Answer: (B) Lang and colleagues give about 52–72% for men and 54–74% for women [2].

Q6. As heart rate rises from 75 to 180 beats per minute:
  1. (A) Systole shortens more than diastole
  2. (B) Diastole shortens much more than systole
  3. (C) Both stay the same
  4. (D) Diastole lengthens

Answer: (B) Diastolic time is squeezed most, limiting filling time at very high rates [1].

Q7. In a pressure–volume loop, the width of the loop represents:
  1. (A) Heart rate
  2. (B) Stroke volume
  3. (C) Blood pressure
  4. (D) Ejection time

Answer: (B) Width is end-diastolic minus end-systolic volume, the stroke volume [1].

Q8. A Cochrane review of exercise-based cardiac rehabilitation in heart failure found that, over the short term, it probably:
  1. (A) Increases hospital admissions
  2. (B) Reduces all-cause hospital admissions
  3. (C) Has no effect on any outcome
  4. (D) Doubles mortality

Answer: (B) Long and colleagues found a reduction in all-cause hospital admissions up to 12 months [3].

Q9. The same Cochrane review found that short-term mortality:
  1. (A) Was halved
  2. (B) Showed little or no difference
  3. (C) Rose sharply
  4. (D) Was not measured

Answer: (B) Little or no difference in all-cause mortality was seen over the short term [3].

Q10. The second heart sound (S2) marks:
  1. (A) The start of systole
  2. (B) Closure of the aortic and pulmonary valves at the end of ejection
  3. (C) Atrial contraction
  4. (D) Opening of the mitral valve

Answer: (B) S2 follows the fall of ventricular pressure below aortic pressure at the end of ejection [1].

Quick review

Key takeaways

  • Two pumps in series; four valves open and close passively by pressure differences.
  • Phases: atrial systole, isovolumetric contraction, ejection, isovolumetric relaxation, filling [1].
  • EDV about 120 mL, ESV about 50 mL, SV about 70 mL; EF about 52–72% (men), 54–74% (women) [2].
  • S1 = AV valves close; S2 = semilunar valves close; S3 and S4 are filling sounds.
  • Higher heart rate shortens diastole most, reducing filling and coronary perfusion time.
  • Exercise rehabilitation in heart failure probably reduces hospital admissions [3].

Further reading

SourceWhy it earns its place
Levick JR — An Introduction to Cardiovascular PhysiologyClear, quantitative account of the cardiac cycle
Hall JE, Hall ME — Guyton and Hall Textbook of Medical PhysiologyStandard cardiac cycle chapter
Mitchell JR, Wang JJ — Advances in Physiology Education, 2014How to read the Wiggers diagram well [1]
Long L et al. — Cochrane Review, 2019Evidence for exercise in heart failure [3]

References

  1. Mitchell JR, Wang JJ. Expanding application of the Wiggers diagram to teach cardiovascular physiology. Advances in Physiology Education. 2014 Jun;38(2):170–175. doi:10.1152/advan.00123.2013 PMID 24913453 Teaching paper
  2. Lang RM, Badano LP, Mor-Avi V, et al. Recommendations for cardiac chamber quantification by echocardiography in adults: an update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging. Journal of the American Society of Echocardiography. 2015 Jan;28(1):1–39.e14. doi:10.1016/j.echo.2014.10.003 PMID 25559473 Guideline
  3. Long L, Mordi IR, Bridges C, et al. Exercise-based cardiac rehabilitation for adults with heart failure. Cochrane Database of Systematic Reviews. 2019 Jan 29;1(1):CD003331. doi:10.1002/14651858.CD003331.pub5 PMID 30695817 Cochrane systematic review

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Reviewed by the Physiotherapist India Team. · Human Physiology contents