The heart and circulation — Edexcel GCSE Combined Science
How the structure of the heart, valves and blood vessels allows blood to circulate, and how to calculate cardiac output.
Revision notes
2 short notes, in the order of the specification. Each one in short:
Humans have a double circulatory system: blood goes from the heart to the lungs and back, then from the heart around the body and back. The right ventricle pumps deoxygenated blood to the lungs through the pulmonary artery, and the left ventricle pumps oxygenated blood to the body through the aorta. Valves prevent backflow.
Cardiac output is the volume of blood pumped out of the heart per minute, in cm³ per minute. It is calculated as cardiac output = stroke volume × heart rate, where stroke volume is the volume pumped in each beat and heart rate is beats per minute. For example, 75 cm³ × 70 bpm = 5250 cm³ per minute.
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Quick check questions
Which vessel carries oxygenated blood from the lungs to the heart?
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The pulmonary vein.
Why is the wall of the left ventricle thicker than the wall of the right ventricle?
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It pumps blood around the whole body, which needs a higher pressure than pumping blood to the lungs.
What is the job of the valves in the heart?
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To prevent backflow and keep blood flowing in one direction.
State the equation for cardiac output.
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Cardiac output = stroke volume × heart rate.
Frequently asked questions
How does the heart pump blood?
Deoxygenated blood enters the right atrium through the vena cava. The right atrium contracts, pushing blood into the right ventricle, which pumps it to the lungs through the pulmonary artery. Oxygenated blood returns through the pulmonary vein to the left atrium, then the left ventricle pumps it around the body through the aorta. Valves prevent backflow.
Why is the left ventricle thicker than the right?
The left ventricle has a thicker, more muscular wall because it pumps blood around the whole body, which needs a higher pressure. The right ventricle pumps blood only to the lungs, which are close by. The higher pressure matters because blood pressure falls as blood passes through the capillaries in the lungs.
What blood vessels carry blood away from the heart?
Arteries carry blood away from the heart. The aorta carries oxygenated blood from the left ventricle to the body, and the pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. So not all arteries carry oxygenated blood: the pulmonary artery is the exception. Veins carry blood towards the heart.
What is a double circulatory system?
A double circulatory system is one in which blood passes through the heart twice on each complete circuit of the body. In humans, one circuit carries blood from the heart to the lungs and back, and the other carries it from the heart around the body and back. Returning to the heart lets the pressure be raised again.
How do you calculate cardiac output?
Cardiac output is calculated by multiplying stroke volume by heart rate. Stroke volume is the volume of blood pumped in each beat, in cm³, and heart rate is in beats per minute, so cardiac output is in cm³ per minute. For example, a stroke volume of 75 cm³ and a heart rate of 70 bpm give 5250 cm³ per minute.
Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026