The heart is a double pump made of muscle. Learn its chambers, valves and blood supply, see how a beat pushes blood out in arteries and draws it back in veins, measure what exercise does to the heart rate, and find out how a blocked coronary artery leads to a heart attack. The valve names, wall thickness, the action of the heart and the explanation of heart rate changes are Extended.
The heart is a muscular pump with a muscular wall, a septum, left and right atria, left and right ventricles, one-way valves and coronary arteries that supply its own muscle. Blood is pumped away from the heart in arteries and returns to the heart in veins. Heart activity can be monitored by an ECG, the pulse rate and listening to the sounds of the valves closing. Blockage of the coronary arteries causes coronary heart disease.
Fig. 1: a vertical section through the heart, seen from the front, so the right side is drawn on the left of the page
Section 01
Chambers, valves and the septum.
Click each part of the cut-away heart, then press Play heartbeats. The Stage of the beat and Valves readouts change as the atria and then the ventricles contract. Keep Slow ticked to follow each step.
Atria (top chambers): receive blood from veins. The right atrium gets deoxygenated blood from the body in the vena cava; the left atrium gets oxygenated blood from the lungs in the pulmonary vein.
Ventricles (bottom chambers): pump blood out into arteries. The right ventricle pumps to the lungs in the pulmonary artery; the left ventricle pumps to the body in the aorta.
Arteries and veins: blood is pumped away from the heart in arteries and returns to the heart in veins.
Coronary arteries: branch from the aorta and run over the surface of the heart, supplying the heart muscle with oxygen and glucose.
Extended, valves: the atrioventricular (AV) valves lie between each atrium and ventricle; the semilunar valves lie at the bases of the aorta and pulmonary artery.
Extended, wall thickness: the left ventricle wall is thicker than the right because it pumps blood at higher pressure all round the body, while the right pumps only to the nearby lungs (and lower pressure protects the lung capillaries). Atria have thinner walls than ventricles because they only push blood a short distance into the ventricles.
Extended, septum: separates the two sides so oxygenated and deoxygenated blood do not mix, and the body receives blood carrying as much oxygen as possible.
Extended: stage of the beat
AV valves
Semilunar valves
What happens
atria contract
open
shut
blood is pushed from the atria into the ventricles
ventricles contract
shut (first sound)
open
pressure shuts the AV valves and forces blood into the aorta and pulmonary artery
heart relaxes
open
shut (second sound)
semilunar valves stop backflow; blood from the veins fills the atria
Examiner trap
Diagrams show the heart as if you are facing the person, so the left ventricle is on the right of the page. Find the thick-walled ventricle or the aorta first, then label left and right.
Section 02
Monitoring the heart and exercise.
Choose resting, walking, jogging or sprinting and watch the ECG trace, the heart rate readout and the graph of heart rate against time. Then pick "stopped: recovering". Press Count the pulse for 15 s to take a pulse count the way you would in class.
Three ways to monitor the heart: an ECG (electrocardiogram) records the electrical activity of the heart muscle; the pulse rate is counted at the wrist or neck; a stethoscope picks up the sounds of the valves closing.
Pulse counts: count beats for 15 s and multiply by 4 to get beats per minute. Repeat and take a mean.
Effect of activity: heart rate rises with the intensity of exercise (in the sim, about 70 at rest, about 95 walking, 135 jogging and 175 sprinting) and falls back towards the resting rate after exercise stops. A fitter person recovers faster.
Investigation: measure resting pulse, exercise for a fixed time at a set intensity, then measure pulse immediately and every minute until it returns to resting. Control the type and duration of exercise; use the same person or matched people.
Extended, explaining the rise: contracting muscles respire faster, so they need more oxygen and glucose and produce more carbon dioxide. The heart beats faster (and harder) so blood delivers oxygen and glucose and removes carbon dioxide more quickly. After vigorous exercise the rate stays high while extra oxygen is supplied to break down lactic acid made by anaerobic respiration.
Examiner trap
Do not write that the heart beats faster "to give the muscles more energy" or "to make more oxygen". Blood delivers oxygen and glucose faster so the muscle cells can release more energy by respiration.
Stage 1 · Learn
Check what the sim just showed you
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Quick check+10 XP
In the heart tab, which valves does the Valves readout show as open while the ventricles contract?
Quick check+10 XP
Clicking the left ventricle in the sim, why is its wall much thicker than the right ventricle?
Quick check+10 XP
In the heart rate tab, what happens to the heart rate when you change from walking to sprinting?
Quick check+10 XP
In the coronary heart disease tab, what happens to the Artery open reading as the years run?
Section 03
Coronary heart disease.
Pick some risk factors, then press Run 40 years. Watch the age rise from 20 and the Artery open reading fall as fatty deposits build up inside the coronary artery. Try it with no risk factors, then with several.
What it is: fatty deposits build up in the walls of the coronary arteries, narrowing the lumen. Less blood reaches the heart muscle. A blood clot can then block the narrowed artery completely.
Heart attack: heart muscle beyond the blockage gets no oxygen or glucose, cannot respire and dies (shown grey in the sim).
Risk factors: diet (high in saturated fat), lack of exercise, stress, smoking, genetic predisposition, age and sex (males are at greater risk). Diet, exercise, stress and smoking can be changed; genes, age and sex cannot.
Diet: eating less saturated fat (and less salt) slows the build-up of fatty deposits; more fibre, fruit and vegetables helps keep blood fats lower.
Exercise: regular exercise strengthens the heart muscle, helps keep body mass and blood pressure down and lowers the level of fats in the blood, all reducing the risk.
Examiner trap
Coronary arteries carry blood to the heart muscle, not blood through the chambers. The heart cannot use the blood inside its chambers for its own oxygen supply, which is why a blocked coronary artery is so serious.
Stage 2 · Exam
Exam-style questions
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
Finish the four checks above to unlock the exam questions
Exam style+20 XP
Which vessel carries blood from the right ventricle?
Exam style+20 XP
Extended: what is the importance of the septum?
Exam style+20 XP
A student counts 33 pulse beats in 15 seconds just after exercise. What is the heart rate?
Exam style+20 XP
Which group lists only risk factors for coronary heart disease that a person can change?
Skill unlocked
The heart, mastered.
This skill is now recorded on your profile. Keep the chain going.