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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 Edexcel GCSE PE specification (1PE0 — Topic 1: Applied Anatomy and Physiology) 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 72 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 72 beats per minute (bpm) |
| Function | Pumps blood to the lungs and body |
Exam Tip: Edexcel 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 (semilunar) valve | Between right ventricle and pulmonary artery | Prevents backflow from pulmonary artery to right ventricle |
| Aortic (semilunar) 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 tricuspid valve is on the right side. The bicuspid valve is on the left. Think "Try Before you Buy" — Tricuspid Before Bicuspid, reading from right to left.
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.
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.
The pulmonary veins (there are four) 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 delivering deoxygenated blood to the right atrium.
The coronary arteries branch off from the aorta and supply the heart muscle itself with oxygenated blood. Without the coronary arteries, the cardiac muscle would not receive the oxygen and nutrients it needs to keep beating. Blockage of a coronary artery can lead to a heart attack (myocardial infarction).
| 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 |
| Coronary arteries | Arteries | Oxygenated blood | Aorta → heart muscle |
Exam Tip: Learn the exceptions: the pulmonary artery carries deoxygenated blood and the pulmonary veins carry oxygenated blood. Edexcel regularly sets questions to catch students who assume all arteries carry oxygenated blood.
Understanding the exact pathway that blood takes through the heart is one of the most important things to learn. 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 E fill:#27ae60,color:#fff
style I fill:#e67e22,color:#fff