Mastering cardiac auscultation requires moving beyond simply identifying S1 and S2 to interpreting the timing, quality, and hemodynamic responses of complex sounds. This guide focuses on the clinical differentiation of advanced auscultatory findings.
1. Differentiating Extra Heart Sounds (S3 vs. S4 vs. Snaps)
The timing of diastolic sounds is the most critical factor for differentiation.
| Sound | Timing | Quality/Pitch | Clinical Association |
| S3 (Ventricular Gallop) | Early diastole (rapid filling) | Low pitch (Bell) | “Sound of Distress”: Associated with volume overload, heart failure (systolic dysfunction), or high-output states. May be heard in normal young children. |
| S4 (Atrial Gallop) | Late diastole (atrial kick) | Low pitch (Bell) | “Sound of Stress”: Associated with stiff/hypertrophic ventricles (AS, HTN, HOCM). Never heard in Atrial Fibrillation. |
| Opening Snap (OS) | Early diastole (after S2) | High pitch (Diaphragm) | Mitral Stenosis: A shorter S2-OS interval indicates more severe stenosis (higher LA pressure). |
| Pericardial Knock | Early diastole | High pitch | Constrictive Pericarditis: Occurs earlier and is sharper than an S3; represents the sudden cessation of ventricular filling. |
2. Advanced Murmur Morphology
The “shape” of a murmur on a phonocardiogram reflects the pressure gradient across the valve.
- Crescendo-Decrescendo (Ejection): Typical of Aortic Stenosis (AS). The later the peak of the murmur, the more severe the stenosis, as it takes longer for the ventricle to generate peak pressure against the narrowed orifice.
- Holosystolic (Plateau): Characteristic of Mitral Regurgitation (MR) or VSD. The pressure gradient between the LV and LA remains high throughout the entire systolic phase.
- Decrescendo (Regurgitant): Typical of Aortic Regurgitation (AR). It begins immediately after S2 and fades as the pressure in the aorta drops and the LV fills.
3. Dynamic Auscultation: The “Stress Test” of the Stethoscope
Physical maneuvers are essential when two murmurs sound similar (e.g., AS vs. HOCM or MR vs. TR).
Preload & Afterload Maneuvers
- Valsalva (Strain Phase): Decreases preload.
- Decreases most murmurs (AS, MR).
- Increases the murmur of HOCM (smaller LV volume allows for more obstruction) and moves the MVP click earlier.
- Squatting: Increases both preload and afterload.
- Increases AR, MR, and AS.
- Decreases HOCM and moves the MVP click later.
- Handgrip: Increases afterload (peripheral resistance).
- Increases left-sided regurgitant murmurs (MR, AR).
- Decreases the murmur of AS and HOCM.
- Respiration (Carvallo’s Sign): * Inspiration increases right-sided murmurs (TR, PS) due to increased venous return.
- Expiration accentuates left-sided murmurs (MR, AR, AS).
4. Complex Clinical Phenomena
- Gallavardin Phenomenon: In elderly patients with calcific AS, the harsh systolic murmur may be heard as a high-pitched, musical sound at the apex, mimicking MR. Differentiate using handgrip (MR increases, AS does not).
- Austin Flint Murmur: A mid-diastolic rumble at the apex heard in severe Aortic Regurgitation. It is caused by the AR jet displacing the mitral valve leaflet, creating a “functional” mitral stenosis.
- Summation Gallop: When a patient has both S3 and S4, usually during tachycardia, the sounds fuse into one loud diastolic sound.
Clinical Tip: Always palpate the Carotid Pulse while auscultating. Murmurs occurring with the upstroke are systolic; those occurring after the peak/closure are diastolic.