The heart: a GCSE diagram guide

A GCSE heart diagram labels its four chambers, the right atrium, right ventricle, left atrium and left ventricle, and the four main blood vessels: the vena cava, pulmonary artery, pulmonary vein and aorta. Blood from the right side goes to the lungs, and blood from the left side goes everywhere else. Diagrams are drawn as if you are facing the person, so the heart's right side is on your left.

The labelled heart diagram

 heart's RIGHT      heart's LEFT
 (on your left)     (on your right)

 vena cava in       pulmonary vein in
 +-------------+   +-------------+
 |  R atrium   |   |  L atrium   |
 +------+------+   +------+------+
        | valve           | valve
 +------v------+   +------v------+
 | R ventricle |   | L ventricle |
 |             |   | thick wall  |
 +-------------+   +-------------+
 pulmonary artery  aorta out
 out (to lungs)    (to body)

The wall down the middle, between the two sides, is the septum. It keeps oxygenated and deoxygenated blood apart. On a full diagram the aorta arches over the top, and the coronary arteries run over the outside of the heart.

The parts and what they do

For AQA GCSE Biology, the blood vessels you need are limited to the aorta, vena cava, pulmonary artery, pulmonary vein and coronary arteries, and you don't need the names of the heart valves. Test yourself on the labels, then press Mark to check them in the course.

Blood flow through the heart

Humans have a double circulatory system: blood passes through the heart twice on each trip round the body. AQA's specification puts it this way: the right ventricle pumps blood to the lungs, where gas exchange takes place, and the left ventricle pumps blood around the rest of the body. In order:

1. Deoxygenated blood from the body enters the right atrium through the vena cava.
2. It passes through a valve into the right ventricle.
3. The right ventricle pumps it out through the pulmonary artery to the lungs, where it picks up oxygen and gives up carbon dioxide.
4. Oxygenated blood comes back through the pulmonary vein into the left atrium.
5. It passes through a valve into the left ventricle.
6. From the left ventricle it is pumped into the aorta and on to the rest of the body.

Why the left ventricle has a thicker wall

The left ventricle pumps blood all the way round the body, so it must produce a much higher pressure. Its wall is thicker, with more muscle. The right ventricle only pumps blood to the lungs, which are close by, and a lower pressure also protects the delicate capillaries around the alveoli. The atria have the thinnest walls of all, because they only push blood into the ventricles just below them.

Valves and the heartbeat

Valves between each atrium and ventricle, and at the exits to the arteries, only open one way. When a ventricle contracts, the valve behind it snaps shut, so blood can only go forward into the artery. The "lub dub" of a heartbeat is the sound of valves closing.

A small group of cells in the right atrium sets the heart's natural resting rate: they act as its pacemaker. If they go wrong, an artificial pacemaker, an electrical device, can be fitted to correct irregularities in the heart rate.

Cardiac output

Cardiac output is the volume of blood the heart pumps each minute. It depends on how much blood each beat pushes out (the stroke volume) and how many beats there are per minute:

A heart rate of 75 beats per minute with a stroke volume of 68 cm³ gives 68 × 75 = 5,100 cm³ per minute, or 5.1 dm³ per minute. Rearranged, a cardiac output of 6,000 cm³ per minute at 80 beats per minute means a stroke volume of 6,000 ÷ 80 = 75 cm³. Try one, then press Mark to check it in the course, or use the cardiac output calculator.

How to draw and label a heart diagram in the exam

• Remember the flip. The heart's right side goes on the left of the page.
• Draw the left ventricle wall thicker than the right.
• Use arrows to show the direction of blood flow if asked.
• Label lines should touch the part exactly, with no arrowheads, and shouldn't cross.

Common mistakes

• Swapping left and right. The diagram is a mirror image: the person's right is your left.
• Saying all arteries carry oxygenated blood. The pulmonary artery carries deoxygenated blood.
• Mixing up the pulmonary artery and vein. Artery away to the lungs, vein back from the lungs.
• Saying the heart muscle gets oxygen from the blood inside it. It is supplied by the coronary arteries.
• Saying the left ventricle is thicker because it holds more blood. Both ventricles pump the same volume; the left needs a higher pressure.

The Human Physiology course has a guided tour of the heart, then moves on to blood vessels and blood. To test this topic under time pressure, try today's GCSE Biology Higher or GCSE Combined Science Higher short timed paper.

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