BiologyICSE Class 10 · Circulatory System

Structure and Working of the Human Heart (ICSE Class 10 Biology)

Updated 16 October 2026 · Fact-checked

The human heart is a four-chambered muscular pump inside the pericardium. Two thin-walled atria receive blood and two thick-walled ventricles pump it out; tricuspid, bicuspid and semilunar valves keep flow one way. Blood passes twice through the heart in each round: pulmonary circulation to the lungs and systemic circulation to the body.

Understand Structure and Working of the Human Heart

Position and covering. The heart lies in the thoracic cavity between the two lungs, tilted slightly to the left, above the diaphragm. It is enclosed in the double-layered pericardium, with pericardial fluid between the layers that reduces friction as the heart beats and protects it from shocks. Say 'around the heart', not 'in' or 'on the wall'.

Four chambers.

Chamber	Receives from	Sends to	Wall
Right atrium	superior and inferior venae cavae (deoxygenated)	right ventricle	thin
Right ventricle	right atrium	pulmonary artery → lungs	thick
Left atrium	pulmonary veins (oxygenated)	left ventricle	thin
Left ventricle	left atrium	aorta → whole body	thickest

The left ventricle has the thickest wall because it must pump blood to every part of the body; the right ventricle pumps only to the nearby lungs. A muscular septum keeps the left (oxygenated) and right (deoxygenated) sides apart.

Valves and their positions.

Tricuspid valve (three flaps): between the right atrium and right ventricle.
Bicuspid (mitral) valve (two flaps): between the left atrium and left ventricle.
Semilunar valves: at the bases of the pulmonary artery and the aorta, stopping backflow into the ventricles.
Chordae tendineae: tendon-like cords joining the flaps of the tricuspid and bicuspid valves to papillary muscles of the ventricle walls; they stop the flaps from being pushed up into the atria when the ventricles contract.
Coronary arteries, branching from the base of the aorta, supply the heart muscle itself.

Working: the heartbeat. Systole = contraction; diastole = relaxation.
1. Both atria fill with blood; atrial systole pushes it into the ventricles.
2. Ventricular systole: pressure closes the tricuspid and bicuspid valves (first sound, 'lubb', long and low) and opens the semilunar valves; blood goes into the pulmonary artery and aorta.
3. Ventricular diastole: the ventricles relax, the semilunar valves snap shut (second sound, 'dubb', short and sharp), and the atria refill.
At about 75 beats per minute one full cycle takes about 0.8 s.

Double circulation. In one complete round of the body, blood passes twice through the heart.

Pulmonary circulation: right ventricle → pulmonary artery → lungs (oxygenated) → pulmonary veins → left atrium.
Systemic circulation: left ventricle → aorta → body organs → venae cavae → right atrium.

Advantage: oxygenated and deoxygenated blood never mix, and the body receives fully oxygenated blood at high pressure, which suits warm-blooded animals with high energy needs.

Pulse and blood pressure (brief). The pulse is the rhythmic stretching of an artery wall with each ventricular systole, felt at the wrist (radial artery); about 72 per minute at rest. Blood pressure is the force of blood on artery walls, normally about 120/80 mm Hg: 120 during ventricular systole, 80 during diastole. It is measured with a sphygmomanometer.

First aid for a heart attack (an idea from the 2024 paper). Make the person lie down in an airy place, loosen tight clothing, and rush them to hospital; read every option in a multiple-select question.

Flow chart. Body → venae cavae → right atrium → tricuspid → right ventricle → semilunar → pulmonary artery → lungs → pulmonary veins → left atrium → bicuspid → left ventricle → semilunar → aorta → body.

Draw-and-label checklist: L.S. of the heart. Drawn as seen from the front, so the right side of the heart is on your left. Four chambers with the left ventricle wall thickest; septum; tricuspid and bicuspid valves with chordae tendineae and papillary muscles; semilunar valves; vessels: superior vena cava, inferior vena cava, pulmonary artery, pulmonary veins, aorta. Arrows show the direction of flow. Use full names: never 'P.A.' or 'S.V.C.'.

Structure and Working of the Human Heart: key facts

Valves: Tricuspid right atrium to right ventricle
Bicuspid (mitral) left atrium to left ventricle
Semilunar bases of pulmonary artery and aorta
Chordae tendineae hold flaps to papillary muscles; Always name both chambers a valve lies between.
Main vessels of the heart: Venae cavae body to right atrium
Pulmonary artery right ventricle to lungs (deoxygenated)
Pulmonary veins lungs to left atrium (oxygenated)
Aorta left ventricle to body; Pulmonary artery and pulmonary veins are the exceptions to the oxygen rule.
Heartbeat and readings: Lubb: AV valves close at ventricular systole
Dubb: semilunar valves close at diastole
Pulse about 72 per minute
BP about 120/80 mm Hg; Systole = contraction; diastole = relaxation.

Tricuspid	right atrium to right ventricle
Bicuspid (mitral)	left atrium to left ventricle
Semilunar	bases of pulmonary artery and aorta
Chordae tendineae	hold flaps to papillary muscles

Venae cavae	body to right atrium
Pulmonary artery	right ventricle to lungs (deoxygenated)
Pulmonary veins	lungs to left atrium (oxygenated)
Aorta	left ventricle to body

How to answer Structure and Working of the Human Heart questions

ICSE gives a heart diagram with blanks, asks the exact location of a valve or the pericardium, the cause of the heart sounds, the meaning of systole and diastole, or the route of double circulation.

1Orient the diagram: the heart's right side is on your left.
2Identify vessels by which chamber they join: right ventricle → pulmonary artery; left ventricle → aorta.
3For a location, use exact prepositions: 'between the left atrium and left ventricle', 'around the heart'.
4For circulation, write each stage with arrows, starting from the chamber named.
5Use full names and check spellings: aorta, pericardium, chordae tendineae.

Structure and Working of the Human Heart in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

A trained heart

Suppose a smartwatch shows a resting heart rate of 60 beats per minute for a trained athlete and 80 for her untrained friend.

How many more times does the friend's heart beat in one hour at rest, and why can the athlete's heart beat more slowly?

Try it first, then show the solutionSolution

Difference per minute: 80 − 60 = 20 beats.
In one hour: 20 × 60 = 1200 more beats.
Training makes the ventricle muscle stronger, so it pumps more blood with each systole.
The same volume of blood per minute is then delivered with fewer beats.

Answer: 1200 more beats an hour; the athlete's stronger heart pumps more blood per beat, so it needs fewer beats.

Memory hook: Stronger pump, slower beat.

A leaky valve

Suppose a doctor hears a 'whooshing' sound after the 'lubb' in a patient and says the bicuspid valve is not closing fully.

Where is this valve, and what goes wrong in the heart?

Try it first, then show the solutionSolution

The bicuspid valve lies between the left atrium and left ventricle.
In ventricular systole it should close, so all blood leaves through the aorta.
If it leaks, some blood is pushed back into the left atrium, making the whooshing sound.
Less blood reaches the body with each beat, so the heart must work harder.

Answer: A leaky bicuspid valve lets blood flow back into the left atrium during ventricular systole.

Memory hook: Valves are one-way doors; a leak means backflow.

Tricks to remember Structure and Working of the Human Heart

Short memory aids. Say each one aloud once, then use it on a question the same day.

Try before you Buy
Tricuspid on the right, Bicuspid on the left: T comes before B as R comes before L when you read the heart from the front.
Use it when: Placing the two AV valves.
Arteries go Away
A for Artery, A for Away from the heart; veins bring blood back.
Use it when: Naming pulmonary artery versus pulmonary vein.
LUBB is Long, DUBB is Done
Lubb = AV valves close at the start of systole; Dubb = semilunar valves close when it is done.
Use it when: Linking heart sounds to valves.

Structure and Working of the Human Heart: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Which valve? · 1 mark · MCQBoard level

The valve that stops blood flowing back from the aorta into the left ventricle is the:
(a) bicuspid valve (b) tricuspid valve (c) semilunar valve (d) mitral valve

Try it first, then show the solutionSolution

Valves at the bases of the aorta and pulmonary artery are semilunar.

Answer: (c) semilunar valve.

Example 2: Exact positions · 2 marks · Short answerBoard level

State the exact position of (a) the semilunar valves and (b) the septum, and (c) name the vessels that open into the right atrium. (The 2024 paper asked exact locations of heart parts.)

Try it first, then show the solutionSolution

(a) At the bases of the pulmonary artery and the aorta; (b) between the right and left sides of the heart, separating the two atria and the two ventricles (1 mark).
(c) The superior vena cava and the inferior vena cava (1 mark).

Answer: (a) Bases of the pulmonary artery and aorta. (b) Between the right and left halves of the heart. (c) Superior and inferior venae cavae.

Example 3: Ventricle versus atrium · 2 marks · Short answerHarder board level

The wall of the right ventricle is thicker than the walls of the atria. Explain why.

Try it first, then show the solutionSolution

The atria only push blood a short distance, down into the ventricles just below them (1 mark).
The right ventricle must pump blood out of the heart through the pulmonary artery to the lungs, which needs more force (1 mark).

Answer: Atria push blood only into the ventricles below; the right ventricle must pump it out to the lungs.

Example 4: Heart sounds · 2 marks · Short answerHarder board level

What causes the 'lubb' and 'dubb' sounds of the heart?

Try it first, then show the solutionSolution

Lubb: closure of the tricuspid and bicuspid valves at the start of ventricular systole (1 mark).
Dubb: closure of the semilunar valves at the start of ventricular diastole (1 mark).

Answer: Lubb: AV valves closing; dubb: semilunar valves closing.

Example 5: Output of the heart · 3 marks · Case-basedHOTS / competency

Suppose each ventricular systole of the left ventricle pumps 70 mL of blood and the heart beats 72 times a minute. (a) Calculate the volume pumped in one minute in litres. (b) How many times does the heart beat in one hour? (c) Why does the right ventricle pump the same volume despite its thinner wall?

Try it first, then show the solutionSolution

(a) 70 × 72 = 5040 mL ≈ 5.04 L per minute (1 mark).
(b) 72 × 60 = 4320 beats (1 mark).
(c) All blood returning from the body must go through the lungs; the right ventricle pumps the same volume but over a short distance at low pressure (1 mark).

Answer: (a) 5.04 L. (b) 4320. (c) Same volume, lower pressure, shorter path to the lungs.

Example 6: Hole in the septum · 3 marks · Short answerHOTS / competency

Suppose a baby is born with a small hole in the septum between the two ventricles. Explain how this affects the oxygen content of blood reaching the body and the baby's energy.

Try it first, then show the solutionSolution

The septum normally keeps oxygenated (left) and deoxygenated (right) blood apart (1 mark).
Through the hole some blood mixes, so blood leaving by the aorta carries less oxygen (1 mark).
Tissues get less oxygen, respiration releases less energy, and the baby tires easily (1 mark).

Answer: Mixing of blood lowers oxygen supply to tissues, so less energy is released and the baby tires easily.

Where students lose marks in Structure and Working of the Human Heart

The slips examiners see most often, and what to write instead.

Mistake: Vague locations
CISCE examiners' comments (2024): candidates said the pericardium is on the wall or in the heart, and placed the bicuspid valve between the right atrium and right ventricle or 'on the left side of the heart'.
Do this: Pericardium around the heart; bicuspid between the left atrium and left ventricle.
Usually costs: 1 mark each.
Mistake: Short forms and swapped vessels on diagrams
CISCE examiners' comments (2025): candidates confused the pulmonary artery and vein, used short forms like P.A., wrote vena cava for aorta, misspelt aorta, wrote pleura for pericardium, and wrote valves or papillary muscles for chordae tendineae.
Do this: Full names, correct spellings; identify vessels by the chamber they join.
Usually costs: 1 mark each.
Mistake: Picking only some correct first-aid options
CISCE examiners' comments (2024): in a heart-attack first-aid question, candidates chose P and Q instead of P, Q and R because they did not read all options.
Do this: Read every option before choosing.
Usually costs: 1 mark.

Exam tips

Right side of the heart is on your left in a diagram.
Name both chambers a valve lies between.
Lubb = AV valves; dubb = semilunar valves.
Pulse about 72 per minute; BP about 120/80 mm Hg.

Practice questions on Structure and Working of the Human Heart

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The vessel that carries blood out of the right ventricle is the:
(a) aorta (b) pulmonary artery (c) pulmonary vein (d) inferior vena cava
Hint
Right side goes to the lungs.
Answer
(b) pulmonary artery.
Q2 · 1 mark · Very short answerBoard level
What would happen during ventricular systole if the chordae tendineae of the tricuspid valve snapped?
Hint
What keeps the flaps from turning inside out?
Answer
The valve flaps would be pushed up into the right atrium, so blood would leak back into the right atrium instead of all going to the pulmonary artery.
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Blood passes through the heart twice in one complete round of the body.
Reason (R): The heart has separate pulmonary and systemic circulations.
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(d) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
Hint
Double circulation.
Answer
(c).
Q4 · 2 marks · Short answerHarder board level
Define systole and diastole.
Hint
Contract, relax.
Answer
Systole is the contraction of the heart chambers that pushes blood out; diastole is their relaxation, during which they fill with blood.
Q5 · 3 marks · Short answerHarder board level
Trace the path of a red blood cell from the right atrium until it leaves the heart through the aorta, naming valves and the organ visited.
Hint
Both circuits.
Answer
Right atrium → tricuspid valve → right ventricle → semilunar valve → pulmonary artery → lungs → pulmonary veins → left atrium → bicuspid valve → left ventricle → semilunar valve → aorta.
Q6 · 1 mark · Very short answerHarder board level
What is the function of the pericardial fluid?
Hint
Friction.
Answer
It reduces friction as the heart beats and protects it from mechanical shock.
Q7 · 1 mark · Very short answerHarder board level
In which circulation, pulmonary or systemic, (a) does blood pass through the aorta, and (b) is the blood leaving the heart deoxygenated?
Hint
Left side to body; right side to lungs.
Answer
(a) Systemic. (b) Pulmonary.
Q8 · 3 marks · Case-basedHOTS / competency
Read and answer.
Suppose a 40-year-old's blood pressure reads 150/95 mm Hg.
(a) What do 150 and 95 stand for? (1)
(b) Compared with the normal 120/80, what is the difference between the two numbers in each case? (1)
(c) Name the instrument used and one lifestyle change to lower the reading. (1)
Hint
Systolic/diastolic.
Answer
(a) 150 = systolic pressure (ventricles contracting); 95 = diastolic (ventricles relaxing). (b) 150 − 95 = 55 mm Hg against 120 − 80 = 40 mm Hg. (c) Sphygmomanometer; regular exercise (or less salt, no smoking, healthy weight).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Which chamber has the thickest wall?Show answer
Left ventricle.
2.Which valve lies between the right atrium and right ventricle?Show answer
Tricuspid valve.
3.What is diastole?Show answer
Relaxation of the heart chambers.
4.Which vessels supply the heart muscle?Show answer
Coronary arteries.
5.Where is the pulse usually felt?Show answer
At the wrist, over the radial artery.

Structure and Working of the Human Heart: frequently asked questions

Is the mitral valve the same as the bicuspid valve?

Yes. Both names mean the two-flapped valve between the left atrium and left ventricle.

Why does the pulmonary artery carry deoxygenated blood?

An artery is defined by carrying blood away from the heart; the pulmonary artery takes deoxygenated blood from the right ventricle to the lungs.

Do I need the pacemaker (SA node)?

It is not named in the 2027 syllabus; focus on structure, valves, vessels, systole, diastole and double circulation.

Which vessels must I name?

Only the main vessels entering and leaving the heart, liver and kidney.