Heart Sounds Auscultation – S1, S2, S3, S4 Explained with Mnemonics

Listening to the heart with a stethoscope—known as auscultation—is one of the oldest and most reliable diagnostic tools in medicine. By interpreting heart sounds, clinicians can identify normal cardiac function, valve closures, and detect early signs of heart disease.

Understanding S1, S2, S3, and S4 sounds, along with knowing where to listen on the chest.

5 Auscultation Areas of the Heart

The heart is best heard at specific anatomical points where valves project their sounds. These are known as the five auscultatory areas.

Mnemonic: “All People Enjoy Time Magazine”

1. Aortic Area – Right 2nd intercostal space (RICS).

2. Pulmonic Area – Left 2nd intercostal space (LICS).

3. Erb’s Point – Left 3rd intercostal space (LICS); best for listening to S1 and S2 equally.

4. Tricuspid Area – Left lower sternal border, 4th intercostal space.

5. Mitral Area – Left 5th intercostal space, medial to the midclavicular line.

Tip: Think “M for Midclavicular and Mitral (5 letters = 5th intercostal space).”

Normal Heart Sounds

S1 – “Lub”

• Produced by closure of tricuspid and mitral valves at the start of systole.
• Best heard at the apex (mitral area).
• Corresponds to ventricular contraction (systole).

S2 – “Dub”

• Produced by closure of aortic and pulmonic valves at the end of systole.
• Best heard at the base (aortic and pulmonic areas).
• Corresponds to ventricular relaxation (diastole).

Summary:

• S1 (Lub) → AV valves close (start of systole).
• S2 (Dub) → Semilunar valves close (end of systole/start of diastole).

Abnormal Heart Sounds

S3 – Ventricular Gallop

• Occurs in early diastole during rapid ventricular filling.
• Sounds like “Lub-dub-dub.”
• Normal in children, young adults, and athletes.
• Abnormal in adults >40, often indicating heart failure or fluid overload.

S4 – Atrial Gallop

• Occurs in late diastole due to atrial contraction against a stiff ventricle.
• Sounds like “Lub-lub-dub.”
• Always pathological in adults.
• Seen in conditions like hypertension, aortic stenosis, left ventricular hypertrophy.

Mnemonics for Heart Sounds

1. Systole vs Diastole

S1 = Lub = Systole begins (ventricular contraction).

S2 = Dub = Diastole begins (ventricular relaxation).

Trick: “COZY RED”

• CO → Contract
• ZY → Systole
• RE → Relax
• D → Diastole

2. Extra Sounds

• S3 → “Early Diastole” = rapid filling.
• S4 → “Late Diastole” = atrial kick into stiff ventricle.

Clinical Relevance of Heart Sounds

When S3 Is Significant

Suggests volume overload:

• Congestive heart failure
• Mitral regurgitation
• High-output states (thyrotoxicosis, anemia)

When S4 Is Significant

Suggests pressure overload and stiff ventricles:

• Hypertension
• Aortic stenosis
• Hypertrophic cardiomyopathy

Murmurs and Extra Sounds

• Murmurs: Caused by turbulent blood flow across narrowed or regurgitant valves.
• Clicks/snaps: Opening snaps in mitral stenosis, ejection clicks in aortic stenosis.
• Pericardial rubs: Scratchy sounds in pericarditis.

Practical Guide to Heart Auscultation

1. Quiet environment – background noise can mask subtle sounds.

2. Stethoscope technique:

• Diaphragm → High-pitched sounds (S1, S2, murmurs of regurgitation).
• Bell → Low-pitched sounds (S3, S4, mitral stenosis murmur).

3. Patient position:

• Sitting up, leaning forward → Best for aortic murmurs.
• Left lateral decubitus → Best for mitral murmurs and S3/S4.

4. Timing with pulse: Palpate carotid artery while listening to correlate systole and diastole.

Table: Summary of Heart Sounds

Sound	Timing	Cause	Normal/Abnormal	Best Heard At
S1	Start of systole	Closure of mitral & tricuspid valves	Normal	Apex (mitral)
S2	Start of diastole	Closure of aortic & pulmonic valves	Normal	Base (aortic, pulmonic)
S3	Early diastole	Rapid ventricular filling	Normal in youth, abnormal in adults (CHF)	Apex
S4	Late diastole	Atrial contraction against stiff ventricle	Always abnormal	Apex (with bell)

Frequently Asked Questions (FAQ)

Q1. What is the difference between S1 and S2 heart sounds?

S1 is caused by closure of AV valves (mitral, tricuspid), while S2 is due to closure of semilunar valves (aortic, pulmonic).

Q2. Is S3 always abnormal?

No. It is normal in children, young adults, and athletes, but abnormal in older adults (suggestive of heart failure).

Q3. What does S4 indicate?

S4 always indicates pathology—usually stiff or hypertrophic ventricles due to hypertension or aortic stenosis.

Q4. What is Erb’s point in auscultation?

The 3rd left intercostal space, where S1 and S2 are best heard together.

Q5. Which position best reveals mitral murmurs?

The left lateral decubitus position with the bell of the stethoscope.