Guide to the S3 Heart Sound
The Third Heart Sound (S3 Gallop)
This guide clarifies the S3 gallop, explaining its physiological basis and clinical implications. Understanding this finding is a key step for students in advanced cardiac assessment.
Anatomy of the S3 Gallop
Timing
Occurs in early diastole, just after S2, during the rapid ventricular filling phase.
Mechanism
Caused by vibrations from the sudden deceleration of blood flow into a ventricle.
Cadence
Creates a three-beat rhythm often compared to the word “Ken-tuck-y” (S1-S2-S3).
Physiological vs. Pathological S3
The clinical significance of an S3 depends on the context. It can be a normal finding or a sign of serious cardiac dysfunction.
Physiological S3 (Normal)
A benign finding caused by rapid filling of a healthy, compliant ventricle.
- Common in children and young adults (<40 years).
- Can be present in athletes.
- Often found during pregnancy due to increased blood volume.
- Typically faint and may disappear when the patient sits up.
Pathological S3 (Abnormal)
A significant sign of ventricular dysfunction or volume overload, especially in adults over 40.
- Hallmark of systolic heart failure.
- Associated with mitral or tricuspid regurgitation.
- Can occur in high-output states (e.g., severe anemia, thyrotoxicosis).
- Often precedes other signs of heart failure decompensation.
Interactive Auscultation Guide
Proper technique is crucial for detecting the low-pitched S3 sound. Click each point to review the key steps.
Click a step to learn more
Select a numbered hotspot on the diagram.
Differentiating S3 from Other Sounds
Distinguishing S3 is key. An S4 gallop is a late diastolic sound (“Ten-nes-see”), while murmurs are prolonged “whooshing” sounds. Accurate identification prevents misdiagnosis.
