FSHP Academy
Exercise Physiology — all lessons

Muscle Physiology

Muscle physiology: excitation–contraction and the sliding filament modelConcentric, eccentric and isometric muscle actionsMotor units, recruitment and rate codingNeuromuscular adaptations to training

Energy Systems

Energy systems overview: how the body makes ATPThe ATP-PC (phosphagen) systemAnaerobic glycolysis and lactateThe aerobic oxidative system

Cardiovascular Physiology

Heart anatomy and the cardiac cycleStroke volume, heart rate and cardiac outputBlood components and oxygen transport

Aerobic Fitness and Intensity

Aerobic fitness concepts and adaptationsVO₂ maxLactate thresholdHeart rate zones and RPE-based intensity control

Heart anatomy and the cardiac cycle

The chambers, valves and conduction system of the heart, and the sequence of pressure and volume changes in each beat — the foundation for understanding cardiac output and exercise responses.

Intermediate Evidence: Established consensus 3 min read Reviewed 2026-10-31 Status: draft

Learning objectives

  • Describe the heart’s chambers, valves and the pulmonary and systemic circuits
  • Trace the electrical conduction pathway
  • Explain the phases of the cardiac cycle with pressure and volume changes
  • Relate EDV, ESV, stroke volume and ejection fraction to exercise

Before this lesson

Why this matters

Heart rate, stroke volume and blood pressure responses to exercise only make sense once you know how a single heartbeat works.

Fundamental concepts

  • Right heart → pulmonary circuit (to lungs). Left heart → systemic circuit (to body).
  • Valves: tricuspid (RA→RV), pulmonary (RV→pulmonary artery), mitral/bicuspid (LA→LV), aortic (LV→aorta). Valves open and close passively in response to pressure differences [openstax2022heart].
  • The left ventricle has the thickest wall because it pumps against systemic pressure.

Blood flow: vena cavae → right atrium → tricuspid → right ventricle → pulmonary valve → lungs → pulmonary veins → left atrium → mitral → left ventricle → aortic valve → aorta.

Electrical conduction

SA node (pacemaker) → atria contract → AV node (brief delay allows ventricular filling) → bundle of His → bundle branches → Purkinje fibres → ventricles contract from the apex upward.

The cardiac cycle

The cardiac cycle: pressures and volume in the left ventricle Top panel: left-ventricular pressure rises during isovolumetric contraction until it exceeds aortic pressure, the aortic valve opens and blood is ejected; pressure then falls during isovolumetric relaxation and the ventricle refills at low pressure. Bottom panel: left-ventricular volume stays constant at about 120 millilitres during isovolumetric contraction, falls to about 50 millilitres during ejection, stays constant during isovolumetric relaxation and then rises during filling. Stroke volume is the difference, about 70 millilitres. Atrial systoleIVCEjectionIVRVentricular filling Aortic pressure LV pressure LV volume EDV ≈ 120 mL ESV ≈ 50 mL aortic valve opens closes 04080120 5085120 Pressure (mmHg) Volume (mL) One beat ≈ 0.8 s at 75 bpm · IVC/IVR = isovolumetric contraction/relaxation
Figure 1. Simplified cardiac cycle for the left ventricle at ~75 bpm: pressures (top) and volume (bottom). — Original diagram, FSHP Academy (schematic, not to scale).
PhaseValvesWhat happens
Atrial systoleAV open, semilunar closedAtria top up the ventricles
Isovolumetric contractionAll closedPressure rises, volume constant (EDV)
EjectionSemilunar openBlood ejected; volume falls to ESV
Isovolumetric relaxationAll closedPressure falls, volume constant
Ventricular fillingAV openPassive filling, most of EDV
SV = EDV − ESV · EF = SV ÷ EDVTypical resting values: EDV ≈ 120 mL, ESV ≈ 50 mL, SV ≈ 70 mL, EF ≈ 55–70%.

Exercise implications

At higher heart rates, diastole shortens more than systole, reducing filling time. Endurance-trained hearts compensate with larger, more compliant ventricles and greater blood volume, raising EDV and stroke volume [levine2008]. See cardiac output.

Common mistakes and misconceptions

Case study

A cyclist notices heart rate rising during long climbs at constant power. The coach explains cardiovascular drift: rising temperature and fluid loss reduce venous return and stroke volume, so HR rises to maintain cardiac output — linking cardiac-cycle mechanics to field data.

Further learning: video lessons

Video links are only marked “verified” after a human has watched them. Unverified entries open a YouTube search for that channel and topic rather than a guessed link.

Introductory needs verification — opens a YouTube search

The heart: anatomy and blood flow

Crash Course

You will understand: chambers, valves and circuits

Why: Clear and engaging.
Technical needs verification — opens a YouTube search

The cardiac cycle (Wiggers diagram)

Ninja Nerd

You will understand: pressure–volume events in each phase

Why: Detailed walkthrough of the diagram.

Knowledge check

Knowledge check · 0/5

1. Oxygenated blood enters the heart through the…

Answer B. Pulmonary veins return oxygenated blood from the lungs to the left atrium.

2. The heart’s natural pacemaker is the…

Answer B. The sinoatrial node in the right atrium initiates each beat.

3. During isovolumetric contraction…

Answer A. Pressure rises with all valves closed until it exceeds aortic pressure.

4. EDV 120 mL and ESV 50 mL give an ejection fraction of about…

Answer B. SV = 70 mL; EF = 70/120 ≈ 58%.

5. As heart rate increases, which phase shortens most?

Answer B. Diastolic (filling) time shortens disproportionately at high heart rates.

Short-answer & application questions

  1. Trace a red blood cell from the right atrium to the aorta, naming each valve.
  2. Why is the left ventricular wall thicker than the right?
  3. How might endurance training change EDV and why?

Key takeaways

  • The heart has four chambers and four valves serving the pulmonary (right) and systemic (left) circuits.
  • The SA node initiates each beat; the impulse passes through the AV node, bundle of His and Purkinje fibres.
  • Each cycle includes filling, isovolumetric contraction, ejection and isovolumetric relaxation.
  • Stroke volume = EDV − ESV; at higher heart rates diastole (filling time) shortens most.

Connected topics

physiology

Stroke volume, heart rate and cardiac output

physiology

Blood components and oxygen transport

physiology

Heart rate zones and RPE-based intensity control

metabolic health

Hypertension training guidelines

References

  1. Betts JG, Young KA, Wise JA, et al. (2022). Anatomy and Physiology 2e — Chapter 19: The Cardiovascular System: The Heart. OpenStax, Rice University. · Link Textbook check pending
  2. Levine BD (2008). V̇O₂max: what do we know, and what do we still need to know?. Journal of Physiology, 586(1):25–34. doi:10.1113/jphysiol.2007.147629 Narrative review check pending

Educational content only — not medical advice. Consult a qualified clinician for diagnosis or treatment.