You are viewing a free preview of this lesson.
Subscribe to unlock all 10 lessons in this course and every other course on LearningBro.
The heart is the central organ of the cardiovascular system, responsible for pumping blood around the body to deliver oxygen and nutrients to working muscles and organs. In this lesson you will learn about the four chambers of the heart, the major blood vessels connected to it, and the valves that ensure blood flows in the correct direction. A thorough understanding of heart structure is essential for the AQA GCSE PE specification (3.1.1.2) and underpins every other lesson in this topic.
The heart is a muscular organ roughly the size of a clenched fist, located slightly to the left of the centre of the chest, between the lungs and behind the sternum (breastbone). It beats approximately 70 times per minute at rest, pumping around 5 litres of blood per minute through the body.
The heart is made of a specialised type of muscle called cardiac muscle. Unlike skeletal muscle, cardiac muscle never fatigues — it contracts rhythmically and involuntarily throughout your entire life, without conscious control.
| Feature | Detail |
|---|---|
| Location | Centre-left of the chest, between the lungs |
| Size | Approximately the size of a clenched fist |
| Muscle type | Cardiac muscle (involuntary, does not fatigue) |
| Resting heart rate | Approximately 70 beats per minute (bpm) |
| Function | Pumps blood to the lungs and body |
Exam Tip: AQA may ask you to label a diagram of the heart. Always remember that diagrams of the heart are drawn as if you are looking at someone else's heart — so the left side of the heart appears on the right side of the diagram, and vice versa.
The heart is divided into four hollow chambers. The upper two chambers are called atria (singular: atrium), and the lower two chambers are called ventricles.
The right atrium is the upper chamber on the right side of the heart. It receives deoxygenated blood (blood that has had its oxygen used up by the body's cells) from two large veins:
When the right atrium contracts, it pushes blood down through the tricuspid valve into the right ventricle.
The right ventricle is the lower chamber on the right side. It receives deoxygenated blood from the right atrium and pumps it through the pulmonary valve into the pulmonary artery, which carries it to the lungs. Here, the blood picks up oxygen and releases carbon dioxide.
The walls of the right ventricle are thinner than those of the left ventricle because the right ventricle only needs to pump blood a short distance to the lungs (the pulmonary circuit).
The left atrium is the upper chamber on the left side. It receives oxygenated blood returning from the lungs via the four pulmonary veins (two from each lung). When it contracts, blood passes down through the bicuspid (mitral) valve into the left ventricle.
The left ventricle is the lower chamber on the left side and is the most powerful chamber of the heart. It has the thickest muscular wall of all four chambers because it must generate enough force to pump oxygenated blood through the aorta and around the entire body (the systemic circuit).
| Chamber | Receives blood from | Sends blood to | Blood type |
|---|---|---|---|
| Right atrium | Superior and inferior vena cava | Right ventricle | Deoxygenated |
| Right ventricle | Right atrium | Pulmonary artery (to lungs) | Deoxygenated |
| Left atrium | Pulmonary veins (from lungs) | Left ventricle | Oxygenated |
| Left ventricle | Left atrium | Aorta (to body) | Oxygenated |
Exam Tip: A very common question is: "Explain why the left ventricle has a thicker muscular wall than the right ventricle." The answer is that the left ventricle must pump blood at a much higher pressure to push it around the entire body (systemic circulation), while the right ventricle only pumps blood the short distance to the lungs (pulmonary circulation).
The septum is a thick muscular wall that divides the heart into left and right halves. It prevents oxygenated and deoxygenated blood from mixing, which is essential for efficient oxygen delivery to the body's tissues.
Valves in the heart are crucial structures that prevent the backflow of blood, ensuring it always flows in one direction. There are four main valves:
| Valve | Location | Function |
|---|---|---|
| Tricuspid valve | Between right atrium and right ventricle | Prevents backflow from right ventricle to right atrium |
| Bicuspid (mitral) valve | Between left atrium and left ventricle | Prevents backflow from left ventricle to left atrium |
| Pulmonary valve | Between right ventricle and pulmonary artery | Prevents backflow from pulmonary artery to right ventricle |
| Aortic valve | Between left ventricle and aorta | Prevents backflow from aorta to left ventricle |
The tricuspid and bicuspid valves are collectively known as atrioventricular (AV) valves because they sit between the atria and ventricles. The pulmonary and aortic valves are known as semilunar valves due to their crescent (half-moon) shape.
Exam Tip: Remember the mnemonic: the tricuspid valve is on the right side (tri = right in many students' memory aids), and the bicuspid valve is on the left. Alternatively, think "Try Before you Buy" — Tricuspid Before Bicuspid, reading from right to left.
There are four major blood vessels connected to the heart that you must know:
The aorta is the largest artery in the body. It carries oxygenated blood away from the left ventricle to the rest of the body. It arches over the top of the heart before descending through the torso, branching into smaller arteries along the way.
The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. This is the only artery in the body that carries deoxygenated blood — a fact that examiners love to test.
The pulmonary veins (there are four of them) carry oxygenated blood from the lungs back to the left atrium. These are the only veins in the body that carry oxygenated blood.
The vena cava is the largest vein in the body. It has two sections — the superior vena cava (upper body) and the inferior vena cava (lower body) — both of which deliver deoxygenated blood to the right atrium.
| Blood Vessel | Type | Carries | From / To |
|---|---|---|---|
| Aorta | Artery | Oxygenated blood | Left ventricle → body |
| Pulmonary artery | Artery | Deoxygenated blood | Right ventricle → lungs |
| Pulmonary veins | Veins | Oxygenated blood | Lungs → left atrium |
| Vena cava | Vein | Deoxygenated blood | Body → right atrium |
Exam Tip: Learn the exceptions: the pulmonary artery carries deoxygenated blood and the pulmonary veins carry oxygenated blood. This is the opposite of what you might expect, and AQA regularly sets questions designed to catch students who assume all arteries carry oxygenated blood and all veins carry deoxygenated blood.
Understanding the exact pathway that blood takes through the heart is one of the most important things to learn for this topic. Here is the complete sequence:
graph TD
A[Vena Cava] -->|Deoxygenated blood from body| B[Right Atrium]
B -->|Through tricuspid valve| C[Right Ventricle]
C -->|Through pulmonary valve| D[Pulmonary Artery]
D -->|To lungs for gas exchange| E[Lungs]
E -->|Oxygenated blood| F[Pulmonary Veins]
F -->|Returns to heart| G[Left Atrium]
G -->|Through bicuspid valve| H[Left Ventricle]
H -->|Through aortic valve| I[Aorta]
I -->|Oxygenated blood to body| J[Body Tissues]
J -->|Deoxygenated blood returns| A
style A fill:#4a90d9,color:#fff
style B fill:#e74c3c,color:#fff
style C fill:#e74c3c,color:#fff
style D fill:#c0392b,color:#fff
style E fill:#27ae60,color:#fff
style F fill:#27ae60,color:#fff
style G fill:#2ecc71,color:#fff
style H fill:#2ecc71,color:#fff
style I fill:#f39c12,color:#fff
style J fill:#f39c12,color:#fff
The heart itself also needs a blood supply to keep the cardiac muscle functioning. The coronary arteries branch off from the aorta and wrap around the surface of the heart, supplying the heart muscle with oxygenated blood and nutrients.
If a coronary artery becomes blocked (for example, by a build-up of fatty deposits called atheroma), the heart muscle downstream of the blockage is starved of oxygen. This can lead to a heart attack (myocardial infarction), where cardiac muscle cells die due to lack of oxygen.
| Term | Meaning |
|---|---|
| Coronary arteries | Arteries that supply the heart muscle itself with oxygenated blood |
| Coronary heart disease | Condition where coronary arteries become narrowed by fatty deposits |
| Heart attack | Death of cardiac muscle cells caused by a blocked coronary artery |
Imagine Nadia, a 17-year-old GCSE PE student completing her first half-marathon. She has trained for 6 months. At mile 11 her heart has pumped roughly 44,000 times since the gun. Let's follow a single red blood cell arriving at her heart at this moment and trace its path through the four chambers, four valves and four major vessels.
Step 1 — into the right atrium. The red blood cell — now deoxygenated after unloading its oxygen in her quadriceps — returns via the vena cava (superior from the head/arms, inferior from the trunk/legs) and flows into Nadia's right atrium. The right atrium has a thin wall because it only needs to push blood a short distance into the right ventricle just below.
Step 2 — through the tricuspid valve into the right ventricle. As the right atrium contracts (atrial systole), the tricuspid valve opens and blood is pushed down into the right ventricle. The wall here is thicker than the atrium, but still thinner than the left ventricle, because it only needs to generate enough pressure to push blood through the pulmonary circuit.
Step 3 — through the pulmonary valve into the pulmonary artery. When the right ventricle contracts (ventricular systole), the tricuspid valve snaps shut (preventing backflow) and the pulmonary valve opens. Blood is ejected into the pulmonary artery — the only artery in the body that carries deoxygenated blood. It travels to both lungs.
Step 4 — gas exchange at the lungs. In the pulmonary capillary beds, CO₂ leaves the blood and O₂ binds to haemoglobin. The red blood cell is now re-saturated with oxygen.
Step 5 — back to the heart via the pulmonary veins. The red blood cell returns through the pulmonary veins — the only veins in the body that carry oxygenated blood — and enters the left atrium.
Step 6 — through the bicuspid valve into the left ventricle. Atrial systole pushes the blood through the bicuspid (mitral) valve into the left ventricle. Crucially, the septum between the right and left sides prevents any mixing of oxygenated and deoxygenated blood.
Step 7 — out through the aortic valve and the aorta. The left ventricle — with its thick muscular wall — contracts and generates the highest pressure in Nadia's entire circulation (~180 mmHg at this intensity). The aortic valve opens and the red blood cell is ejected into the aorta at high pressure, ready to travel all the way back down her legs to fuel her quadriceps for the final mile.
Why structure matches function. Nadia's left ventricle has the thickest wall because it must pump blood through the systemic circuit (the whole body). Her right ventricle has a thinner wall because it only pumps through the pulmonary circuit (lungs, much shorter). The four valves stop backflow, the septum prevents mixing, and the coronary arteries (branching off the aorta just above the aortic valve) supply her own heart muscle — because the heart cannot use the blood inside its chambers to oxygenate itself.
The takeaway. Nadia's mile 22 illustrates (1) the four chambers and their relative wall thicknesses, (2) the four valves in the correct order, (3) the four major vessels, (4) the two circuits, and (5) the role of the coronary arteries.
Misconception: "Arteries always carry oxygenated blood and veins always carry deoxygenated blood."
Reality: This is true everywhere except in the pulmonary circuit. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs, and the pulmonary veins carry oxygenated blood from the lungs to the left atrium. The definition of an artery is a vessel that carries blood away from the heart, and a vein is one that carries blood towards the heart — it has nothing to do with oxygen content. This is one of the most commonly lost marks in the heart labelling question.
Example 6-mark question: "Describe the structure of the heart and explain how its structure is adapted to its function." (6 marks)
Grade 3–4 response (typically 2–3 marks)
The heart has four chambers and pumps blood around the body. It has valves to stop blood going the wrong way. The left side is bigger because it pumps further.
Examiner comment: AO1 shows very basic recall — names chambers and valves in general terms and identifies the left/right size difference. Missing precise vocabulary (atrium/ventricle, tricuspid/bicuspid/semilunar, septum, major vessels). Two to three marks typical.
Grade 5–6 response (typically 4–5 marks)
The heart has four chambers: the right atrium and right ventricle (which pump deoxygenated blood to the lungs through the pulmonary artery) and the left atrium and left ventricle (which pump oxygenated blood to the body through the aorta). There are four valves: the tricuspid and bicuspid valves prevent backflow from ventricles to atria, and the pulmonary and aortic (semilunar) valves prevent backflow from arteries to ventricles. The septum separates the two sides and stops oxygenated and deoxygenated blood from mixing. The left ventricle has the thickest wall because it must pump blood at high pressure to every part of the body.
Examiner comment: Solid AO1 + AO2, correctly naming chambers, valves, septum and explaining the left-ventricle wall thickness. Could push into the top band by including the vena cava and pulmonary veins, and by linking structure to exercise demand (AO3).
Grade 7–9 response (typically 5–6 marks)
The heart is a four-chambered muscular pump. Deoxygenated blood returns from the body via the superior and inferior vena cava into the right atrium, passes through the tricuspid valve into the right ventricle, and is pumped through the pulmonary valve into the pulmonary artery to the lungs. Oxygenated blood returns via the pulmonary veins into the left atrium, passes through the bicuspid valve into the left ventricle, and is ejected through the aortic valve into the aorta for distribution around the body. The septum prevents mixing, maintaining efficient oxygen delivery. The left ventricle has the thickest myocardial wall because it generates the high pressure required to pump blood through the systemic circuit (whole body), while the right ventricle wall is thinner because the pulmonary circuit is shorter and lower pressure (AO2). The coronary arteries branch from the aorta to supply the heart muscle itself with oxygenated blood — essential during exercise when cardiac workload rises sharply (AO3). Together these features ensure a one-way, separated, high-pressure circulation that can scale from ~5 l/min at rest to over 25 l/min during maximal exercise.
Examiner comment: Full AO1/AO2/AO3: precise anatomical vocabulary, all four vessels and valves, septum, wall thicknesses linked explicitly to pressure demands, coronary arteries linked to exercise, and an evaluative comment on scalability of Q. Top band AQA mark-scheme language.
This content is aligned with the AQA GCSE Physical Education (8582) specification, Paper 1: The human body and movement in physical activity and sport — The cardio-respiratory system. For the most accurate and up-to-date information, please refer to the official AQA specification document.