Cardiac cycle: third heart sound: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Cardiac cycle: third heart sound

Sample item

A 62-year-old man with orthopnoea and bibasal crepitations has a low-pitched sound heard at the apex shortly after the second heart sound. What produces this sound?

AOpening of a stenosed mitral valveBRapid passive ventricular filling in early diastoleCClosure of the mitral and tricuspid valves at the start of systoleDAtrial contraction into a stiff ventricle in late diastole

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Rapid passive ventricular filling in early diastole

The third heart sound arises when blood enters a dilated, volume-loaded ventricle in the rapid filling phase and sets the walls vibrating. It can be normal in children, athletes and pregnancy but indicates heart failure in an older adult (ventricular gallop). A fourth sound is presystolic and reflects a stiff ventricle.

Option by option

A. Opening of a stenosed mitral valve
An opening snap is a high-pitched click from a stenosed valve and is not a low-pitched ventricular sound.
B. Rapid passive ventricular filling in early diastole (correct)
Correct. Rapid early filling of a distended ventricle produces the S3 gallop.
C. Closure of the mitral and tricuspid valves at the start of systole
This describes the first heart sound, which is not early diastolic.
D. Atrial contraction into a stiff ventricle in late diastole
This is the fourth heart sound, which occurs just before S1.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is B, Rapid passive ventricular filling in early diastole. The third heart sound arises when blood enters a dilated, volume-loaded ventricle in the rapid filling phase and sets the walls vibrating.

Why is "Opening of a stenosed mitral valve" not the answer?

An opening snap is a high-pitched click from a stenosed valve and is not a low-pitched ventricular sound.

Why is "Closure of the mitral and tricuspid valves at the start of systole" not the answer?

This describes the first heart sound, which is not early diastolic.

Why is "Atrial contraction into a stiff ventricle in late diastole" not the answer?

This is the fourth heart sound, which occurs just before S1.

What concept does this question test?

It tests Cardiac cycle: third heart sound in Physiology. It can be normal in children, athletes and pregnancy but indicates heart failure in an older adult (ventricular gallop). A fourth sound is presystolic and reflects a stiff ventricle.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Cardiac cycle: third heart sound?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.