Concept Tested:
Identification of low-frequency vs high-frequency heart sounds and correct use of the stethoscope (bell vs diaphragm).
The bell transmits low-pitched sounds, while the diaphragm amplifies high-pitched sounds.
What CMS is assessing here:
- Practical bedside examination skill
- Frequency-based classification of heart sounds
- Identification of diastolic murmurs
Why this matters for the exam
CMS frequently asks applied clinical questions. Many students remember sounds but forget which instrument side to use – a common trap area.
Sounds Best Heard with the Bell (Low-Pitched)
These are low-frequency vibrations:
- Third heart sound (S3) – ventricular filling sound
- Fourth heart sound (S4) – atrial kick against stiff ventricle
- Mid-diastolic murmur of Mitral Stenosis – low rumbling murmur
- Tricuspid mid-diastolic murmur
- Low-pitched Austin Flint murmur
- Some cases of early diastolic rumble in severe AR
Best heard with light pressure at the apex (patient in left lateral position).
Sounds Best Heard with the Diaphragm (High-Pitched)
- Opening snap
- Systolic click (MVP)
- Ejection click
- Early diastolic murmur of Aortic Regurgitation
- Most systolic murmurs (MR, AR, AS)
Quick revision takeaway:
- Bell = Low pitch = S3, S4, MS murmur
- Diaphragm = High pitch = clicks, snaps, AR murmur
- Apply light pressure with bell (firm pressure converts it into diaphragm effect)
- S3 → volume overload
- S4 → pressure overload