Question
A 63-year-old man presents with gradually worsening breathlessness during exertion. On cardiac auscultation, an extra early diastolic sound is heard (third heart sound), while lung examination is normal. Which of the following conditions is most likely associated with this finding?
a) Restrictive cardiomyopathy
b) Dilated cardiomyopathy
c) Atrial fibrillation
d) Mitral stenosis
e) Physiological ageing change
Answer
Dilated cardiomyopathy
Explanation (Corrected High-Yield Version)
A third heart sound (S3) is produced in early diastole due to rapid passive filling of a dilated, volume-overloaded ventricle. It reflects increased filling pressures and impaired systolic function.
In older adults, an S3 is almost always pathological and is classically associated with left ventricular failure and Dilated cardiomyopathy. The dilated ventricle allows sudden deceleration of blood during rapid filling, producing the characteristic “ventricular gallop.”
Clarification of key options:
- Restrictive cardiomyopathy → typically produces S4 due to a stiff ventricle
- Atrial fibrillation → important correction:
- S4 is absent (no coordinated atrial contraction)
- S3 can still be present if there is underlying ventricular dysfunction or heart failure
- However, AF itself does not explain S3 → underlying structural disease does
- Mitral stenosis → causes loud S1, opening snap, mid-diastolic murmur, not S3
- Normal ageing → S3 is not normal in elderly
👉 Therefore, the presence of S3 in this clinical setting most strongly points to dilated cardiomyopathy.
Cheat Sheet (Exam Gold)
- S3 = early diastole → rapid ventricular filling → volume overload
- S4 = late diastole → atrial contraction → stiff ventricle
- S3 in elderly = always think heart failure / DCM
- AF:
- ❌ No S4 (no atrial kick)
- ✅ S3 possible (if LV dysfunction present)
Flashcards
Q: What produces S3?
A: Rapid ventricular filling into a dilated ventricle
Q: S3 in elderly suggests what?
A: Heart failure or dilated cardiomyopathy
Q: Why is S4 absent in AF?
A: No coordinated atrial contraction
Q: Can S3 occur in AF?
A: Yes, if underlying LV dysfunction is present
Q: S3 vs S4 key difference?
A: S3 = volume overload, S4 = pressure overload
MCQs
- A third heart sound occurs due to:
a) Atrial contraction
b) Valve closure
c) Rapid ventricular filling
d) Turbulent systolic flow
Answer: c
Explanation: S3 is an early diastolic sound due to rapid filling.
- In elderly patients, S3 most strongly suggests:
a) Normal variant
b) Hypertrophic cardiomyopathy
c) Dilated cardiomyopathy
d) Mitral stenosis
Answer: c
Explanation: S3 in elderly is pathological → DCM or HF.
- Which statement about atrial fibrillation is TRUE?
a) Produces S4
b) Always produces S3
c) Eliminates S4 but S3 may be present
d) Produces opening snap
Answer: c
Explanation: AF abolishes S4 but S3 can occur if LV dysfunction exists.
- Which condition is most associated with S4?
a) Dilated cardiomyopathy
b) Hypertension
c) Mitral regurgitation
d) Heart failure with reduced EF
Answer: b
Explanation: S4 = stiff ventricle → hypertension, AS, HOCM.
- Which of the following is FALSE?
a) S3 occurs in early diastole
b) S3 indicates volume overload
c) S3 is normal in elderly
d) S3 may occur in heart failure
Answer: c
Explanation: S3 is not normal in elderly.
- Which murmur/sign is typical of mitral stenosis?
a) S3 gallop
b) Opening snap
c) Continuous murmur
d) Ejection click
Answer: b
Explanation: MS → loud S1 + opening snap + diastolic rumble.
- Loss of which heart sound is characteristic of atrial fibrillation?
a) S1
b) S2
c) S3
d) S4
Answer: d
Explanation: S4 requires atrial contraction → absent in AF.
Summary for Quick Exam Revision
A third heart sound (S3) is an early diastolic sound produced by rapid ventricular filling into a dilated, volume-overloaded ventricle. It is physiological in young individuals but pathological in older adults, where it strongly indicates heart failure or dilated cardiomyopathy. The mechanism involves increased filling pressures and reduced ventricular compliance, leading to vibration during early diastole. In contrast, S4 occurs due to atrial contraction against a stiff ventricle and is seen in conditions such as hypertension, aortic stenosis, and hypertrophic cardiomyopathy. Importantly, in atrial fibrillation, S4 is absent due to loss of atrial contraction, but S3 can still be present if there is underlying ventricular dysfunction. Mitral stenosis produces an opening snap and diastolic murmur rather than S3. Therefore, in an elderly patient with exertional dyspnoea and an S3, dilated cardiomyopathy remains the most likely diagnosis.