Question:
All of the following statements about the third heart sound (S3) are true, except:
All of the following statements about the third heart sound (S3) are true, except:
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S3 is early diastole; the sound tied to atrial contraction is a different one.
Updated On: Jun 24, 2026
- Occurs due to rapid filling of the ventricles during atrial systole
- Seen in constrictive pericarditis
- Seen in atrial septal defect (ASD)
- Seen in ventricular septal defect (VSD)
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The Correct Option is A
Solution and Explanation
Step 1: The third heart sound (S3) is a low-pitched diastolic sound. The concept tested is the exact phase of diastole in which it is produced.
Step 2: S3 occurs in early diastole during the rapid passive filling phase of the ventricles, just after the atrioventricular valves open. It is NOT due to atrial systole. The sound caused by atrial contraction (late diastole) is the fourth heart sound (S4). So option A is the false statement.
Step 3: Why the others are true. A pathological S3 reflects a volume-overloaded or stiff filling ventricle. In constrictive pericarditis the abrupt halt to filling produces a loud early diastolic sound called the pericardial knock, which is an S3 equivalent (option B true).
Step 4: ASD and VSD increase volume flow across the AV valves. The high diastolic inflow produces an audible S3 in these left-to-right shunt lesions (options C and D true).
Step 5: Only the timing statement is wrong, because S3 belongs to rapid early diastolic filling, not atrial systole.
Answer: A. Occurs due to rapid filling of the ventricles during atrial systole.
Step 2: S3 occurs in early diastole during the rapid passive filling phase of the ventricles, just after the atrioventricular valves open. It is NOT due to atrial systole. The sound caused by atrial contraction (late diastole) is the fourth heart sound (S4). So option A is the false statement.
Step 3: Why the others are true. A pathological S3 reflects a volume-overloaded or stiff filling ventricle. In constrictive pericarditis the abrupt halt to filling produces a loud early diastolic sound called the pericardial knock, which is an S3 equivalent (option B true).
Step 4: ASD and VSD increase volume flow across the AV valves. The high diastolic inflow produces an audible S3 in these left-to-right shunt lesions (options C and D true).
Step 5: Only the timing statement is wrong, because S3 belongs to rapid early diastolic filling, not atrial systole.
Answer: A. Occurs due to rapid filling of the ventricles during atrial systole.
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