Cardiac Cycle & ECG — NEET Biology MCQs with Solutions
Free NEET Biology Cardiac Cycle & ECG MCQs with step-by-step solutions (67 questions). Part of Body Fluids and Circulation. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Cardiac Cycle & ECG · easy · theory
The volume of blood pumped out by one ventricle in one heartbeat is the:
A. Cardiac output
B. Residual volume
C. Vital capacity
D. Stroke volume ✓ Correct
Solution: Stroke volume (~70 mL) is the blood ejected per beat by a ventricle.
Q2 — Cardiac Cycle & ECG · easy · theory
In an ECG, the ______ wave represents the depolarisation of the ventricles:
A. P wave
B. QRS complex ✓ Correct
C. U wave
D. T wave
Solution: The QRS complex marks ventricular depolarisation (leading to contraction).
Q3 — Cardiac Cycle & ECG · medium · theory
Cardiac output is calculated as:
A. Stroke volume + heart rate
B. Heart rate ÷ stroke volume
C. Stroke volume − heart rate
D. Stroke volume × heart rate ✓ Correct
Solution: Cardiac output = stroke volume × heart rate (~70 mL × 72/min ≈ 5 L/min).
Q4 — Cardiac Cycle & ECG · medium · theory
The P wave of an ECG corresponds to the ______, and the T wave to the ______:
A. Atrial depolarisation; ventricular repolarisation ✓ Correct
B. Ventricular contraction; atrial relaxation
C. Atrial repolarisation; ventricular depolarisation
D. Ventricular repolarisation; atrial depolarisation
Solution: P = atrial depolarisation; QRS = ventricular depolarisation; T = ventricular repolarisation.
Q5 — Cardiac Cycle & ECG · hard · theory
The first heart sound "lubb" is produced by the closure of the ______ valves at the start of ventricular systole:
A. Semilunar
B. Mitral only
C. Atrioventricular (bicuspid and tricuspid) ✓ Correct
D. Aortic and pulmonary
Solution: "Lubb" (S1) = closure of AV valves (systole begins); "dup" (S2) = closure of semilunar valves (systole ends).
Q6 — Cardiac Cycle & ECG · hard · theory
If a person has a heart rate of 75 beats/min and a stroke volume of 70 mL, the cardiac output is:
A. 5.25 L/min ✓ Correct
B. 52.5 L/min
C. 1.05 L/min
D. 145 mL/min
Solution: CO = 75 × 70 = 5250 mL/min = 5.25 L/min.
Q7 — Cardiac Cycle & ECG · easy · numerical
If an adult has a heart rate of 72 beats per minute and a stroke volume of about 70 mL, the cardiac output is approximately:
A. About 0.5 litre per minute
B. About 1 litre per minute
C. About 72 litres per minute
D. About 5 litres per minute ✓ Correct
Solution: Cardiac output = heart rate × stroke volume = 72 × 70 mL ≈ 5040 mL ≈ 5 L/min, the normal resting value.
Q8 — Cardiac Cycle & ECG · easy · numerical
In a normal ECG, the QRS complex represents:
A. Depolarisation of the ventricles, just before their contraction ✓ Correct
B. Repolarisation of the ventricles
C. Closure of the semilunar valves
D. Depolarisation of the atria only
Solution: The QRS complex marks ventricular depolarisation, which initiates ventricular contraction (systole). Ventricular repolarisation is the T wave.
Q9 — Cardiac Cycle & ECG · easy · numerical
The first heart sound, "lubb", is produced by the:
A. Closure of the atrioventricular (tricuspid and bicuspid) valves at the start of ventricular systole ✓ Correct
B. Contraction of the atria during diastole
C. Closure of the semilunar valves at the end of ventricular systole
D. Opening of the semilunar valves during systole
Solution: The "lubb" (first sound) is caused by closure of the AV valves as the ventricles begin to contract; the "dupp" (second sound) is due to semilunar valve closure.
Q10 — Cardiac Cycle & ECG · easy · numerical
Stroke volume is best defined as the volume of blood:
A. Pumped out by each ventricle during one heartbeat ✓ Correct
B. Remaining in the ventricle after contraction
C. Returned to the atria from the veins per minute
D. Pumped by both ventricles together in one minute
Solution: Stroke volume is the amount of blood ejected by a ventricle in a single beat (~70 mL). The one-minute output of a ventricle is the cardiac output.
Q11 — Cardiac Cycle & ECG · medium · numerical
During the ventricular systole phase of the cardiac cycle, which set of valve states is correct?
A. AV valves closed and semilunar valves open ✓ Correct
B. Both AV and semilunar valves open
C. AV valves open and semilunar valves closed
D. Both AV and semilunar valves closed throughout
Solution: When the ventricles contract, rising pressure shuts the AV valves (preventing backflow to atria) and forces the semilunar valves open so blood is ejected into the aorta and pulmonary artery.
Q12 — Cardiac Cycle & ECG · medium · numerical
The sino-atrial node is called the pacemaker of the heart because:
A. It physically pushes blood into the aorta
B. It is the only part of the heart that receives blood from the coronary arteries
C. It generates action potentials at the fastest intrinsic rate, setting the heart rhythm ✓ Correct
D. It repolarises the ventricles during the T wave
Solution: The SAN self-depolarises fastest of all cardiac tissue, so it drives each heartbeat and sets the pace; other regions follow its rhythm.
Q13 — Cardiac Cycle & ECG · medium · numerical
A patient shows a normal ECG except that the T wave is abnormal. This most directly indicates a problem with:
A. Closure of the atrioventricular valves
B. Depolarisation of the atria
C. Conduction through the bundle of His only
D. Repolarisation of the ventricles ✓ Correct
Solution: The T wave corresponds to ventricular repolarisation, so an abnormal T wave points to disturbed ventricular recovery, not atrial depolarisation (P wave).
Q14 — Cardiac Cycle & ECG · medium · numerical
Match each ECG feature with what it signifies and choose the correct set: (i) P wave (ii) QRS complex (iii) T wave — (p) ventricular repolarisation (q) atrial depolarisation (r) ventricular depolarisation.
A. i-q, ii-r, iii-p ✓ Correct
B. i-r, ii-q, iii-p
C. i-p, ii-q, iii-r
D. i-q, ii-p, iii-r
Solution: The P wave = atrial depolarisation, the QRS complex = ventricular depolarisation, and the T wave = ventricular repolarisation.
Q15 — Cardiac Cycle & ECG · medium · numerical
An athlete has a resting heart rate of 50 beats per minute but the same cardiac output (~5 L/min) as an average person. Compared with an untrained individual, the athlete must have a:
A. Stroke volume identical to the untrained person at 70 mL
B. Larger stroke volume of about 100 mL per beat ✓ Correct
C. Cardiac output of about 2.5 L/min
D. Smaller stroke volume of about 30 mL per beat
Solution: Cardiac output = HR × SV; to keep 5 L/min at 50 bpm, stroke volume must be 5000 ÷ 50 = 100 mL, larger than the usual ~70 mL — a hallmark of a trained heart.
Q16 — Cardiac Cycle & ECG · medium · numerical
Assertion (A): The joint diastole is the phase when all four heart chambers are relaxed. Reason (R): During this phase blood flows passively from the atria into the ventricles through the open AV valves. Choose the correct option.
A. A is false but R is true
B. Both A and R are true and R is the correct explanation of A ✓ Correct
C. A is true but R is false
D. Both A and R are true but R is not the correct explanation of A
Solution: In joint diastole all chambers relax, the semilunar valves are shut, and the AV valves are open so blood flows passively from atria into ventricles — R correctly explains the filling that occurs in A.
Q17 — Cardiac Cycle & ECG · easy
The duration of cardiac cycle in a normal man is
A. 60 seconds
B. 0.8 seconds ✓ Correct
C. 80 seconds
D. 72 seconds
Solution: One cardiac cycle lasts about 0.8 seconds in a normal person with a heart rate of about 72 beats per minute.
Q18 — Cardiac Cycle & ECG · medium
During systole of the heart
A. Auricles and ventricles contract separately ✓ Correct
B. Auricles and ventricles contract simultaneously
C. only atria contract
D. only ventricles contract
Solution: Systole includes both atrial and ventricular contraction, but they occur separately (atrial systole precedes ventricular systole), not simultaneously.
Q19 — Cardiac Cycle & ECG · easy
During ventricular systole
A. Oxygenated blood is pumped into aorta and deoxygenated blood is pumped into pulmonary vein
B. Oxygenated blood is pumped into the pulmonary artery and deoxygenated blood is pumped into the artery
C. Oxygenated blood is pumped into the aorta and deoxygenated blood is pumped into the pulmonary artery ✓ Correct
D. Oxygenated blood is pumped into pulmonary vein and deoxygenated blood is pumped into pulmonary artery
Solution: The left ventricle pumps oxygenated blood into the aorta and the right ventricle pumps deoxygenated blood into the pulmonary artery.
Q20 — Cardiac Cycle & ECG · easy
Contraction of right ventricle pumps blood into
A. Pulmonary artery ✓ Correct
B. Dorsal aorta
C. Pulmonary vein
D. Coronary artery
Solution: The right ventricle pumps deoxygenated blood into the pulmonary artery, which carries it to the lungs.
Q21 — Cardiac Cycle & ECG · medium
When ventricular systole occurs
A. Semilunar valves guarding pulmonary artery and aorta are forced to open
B. Tricuspid and bicuspid valves close
C. All the above ✓ Correct
D. Auricular diastole coincides
Solution: During ventricular systole the AV valves close, semilunar valves are forced open, and the atria are in diastole.
Q22 — Cardiac Cycle & ECG · medium
During cardiac cycle about ______ % of ventricular filling occurs prior to atrial contraction and ______ % ventricular filling occurs due to atrial contraction.
A. 10, 90
B. 70, 30 ✓ Correct
C. 30, 70
D. 50, 50
Solution: About 70% of ventricular filling is passive before atrial contraction, and the remaining 30% is added by atrial systole.
Q23 — Cardiac Cycle & ECG · hard
Which of the following events do not occur during joint diastole? I. All 4 chambers of heart are in relaxed state. II. Tricuspid and bicuspid valves open. III. Action potential is conducted from SAN to AVN. IV. Blood from the pulmonary veins and vena cava flows into the left and right ventricles respectively through the left and right atria. V. The semilunar valves are closed.
A. Only I and II
B. Only IV
C. Only III ✓ Correct
D. Only V
Solution: During joint diastole the heart is relaxed and blood flows passively; the SAN-to-AVN action potential belongs to systole, so event III does not occur here.
Q24 — Cardiac Cycle & ECG · easy
Cardiac output is determined by
A. Heart rate
B. Both 1 and 2 ✓ Correct
C. Blood flow
D. Stroke volume
Solution: Cardiac output equals stroke volume multiplied by heart rate, so both determine it.
Q25 — Cardiac Cycle & ECG · easy
The amount of blood to be pumped out by each ventricle per minute is
A. Cardiac output ✓ Correct
B. Stroke volume
C. Residual volume
D. Tidal volume
Solution: Cardiac output is the volume of blood pumped by each ventricle per minute (about 5 litres).
Q26 — Cardiac Cycle & ECG · easy
During cardiac cycle each ventricle pumps out about 70 ml of blood which is called
A. Stroke volume ✓ Correct
B. Residual volume
C. Tidal volume
D. Cardiac output
Solution: The volume pumped by a ventricle in one beat (about 70 ml) is the stroke volume.
Q27 — Cardiac Cycle & ECG · hard
A red blood cell entering the right side of the heart passes by through the following structures: 1. Atrioventricular valves, 2. Semi-lunar valves, 3. Right atrium, 4. Right ventricle, 5. SAN.
A. 3 1 5 2 4
B. 5 3 1 4 2
C. 2 3 1 4 5
D. 3 5 1 2 4 ✓ Correct
Solution: Blood enters the right atrium (3), passes the SAN (5) located in the atrial wall, through the AV valve (1), then reaches the ventricle and the semilunar valve, giving 3 5 1 2 4.
Q28 — Cardiac Cycle & ECG · medium
Cardiac output is
A. SV × HR = 72 ml/min
B. Stroke volume (SV) × Heart rate (HR) = 5 L/min ✓ Correct
C. SV × HR = 500 ml
D. SV × HR = 70 ml/min
Solution: Cardiac output = stroke volume (~70 ml) × heart rate (~72/min) ≈ 5 litres per minute.
Q29 — Cardiac Cycle & ECG · medium
Which of the following statements is not true?
A. In each minute a single cardiac cycle is performed ✓ Correct
B. Cardiac output of an athlete is much higher than that of an ordinary man
C. Cardiac cycle includes auricular systole, ventricular systole and joint diastole/complete diastole
D. Cardiac sounds are of clinical diagnostic significance
Solution: About 72 cardiac cycles occur per minute, not a single one, so that statement is untrue.
Q30 — Cardiac Cycle & ECG · easy
First cardiac sound (lub) is associated with
A. Opening of tricuspid and bicuspid valves
B. Closure of tricuspid and bicuspid valves ✓ Correct
C. Closure of semilunar valves
D. Opening of semilunar valves
Solution: The first heart sound 'lub' is produced by the closure of the atrioventricular (tricuspid and bicuspid) valves at the start of ventricular systole.