Heart sounds: S1, S2 and its splitting, S3 and S4 !

Sign

The heart's two normal beats are its valves closing; extra sounds point to stiff or overloaded ventricles.

Updated 2026-11-01

See it in 3D: Mitral anterior leaflet · Tricuspid septal leaflet · Aortic left coronary cusp · Pulmonary left cusp · Chordae tendineae

What it is

S1 marks the start of systole and S2 its end. Splitting of S2 with breathing is normal; its variants point to bundle branch blocks, shunts or pulmonary hypertension. S3 and S4 are the gallops: they tell how the ventricle fills.

The anatomy it tests

S1: closure of the mitral and tricuspid valves as ventricular contraction begins.
S2: closure of the aortic (A2) and pulmonic (P2) valves. On inspiration more blood returns to the right ventricle, the pulmonic valve closes later and S2 splits.
S3: early diastole, rapid filling striking a dilated or volume-loaded ventricle.
S4: late diastole, atrial contraction against a stiff ventricle; it needs an atrial kick (absent in atrial fibrillation).

How to elicit it

Listen at the four areas while feeling the carotid pulse: the sound that coincides with the pulse is S1.
S1 is loudest at the apex; S2 at the base (aortic and pulmonic areas).
For S2 splitting, listen at the pulmonic area during quiet breathing: it splits on inspiration and fuses on expiration.
For S3 and S4, turn the patient to the left lateral decubitus and rest the bell lightly on the apex.
Record the intensity of S1 and S2, the type of splitting and any extra sound (gallop, click, opening snap).

What a positive result means

Loud S1: mitral stenosis, short PR, tachycardia. Soft S1: long PR, mitral regurgitation, poor ventricular function.
Loud P2: pulmonary hypertension. Soft A2: severe aortic stenosis.
Wide splitting (persists in expiration, widens on inspiration): right bundle branch block, pulmonic stenosis.
Fixed splitting (no change with breathing): atrial septal defect.
Paradoxical splitting (appears on expiration): left bundle branch block, severe aortic stenosis.
S3 after age 40: heart failure with a dilated or volume-overloaded ventricle; may be normal in children, young adults, athletes and pregnancy.
S4: hypertrophied or stiff ventricle (hypertension, aortic stenosis, hypertrophic cardiomyopathy, ischemia).

Usefulness and limits

S3 and S4 are low-pitched and soft: they are missed with the diaphragm alone.
Inter-observer agreement for gallops is moderate; echocardiography defines ventricular function.

Test yourself

Think of the answer, then tap the question to see it.

Which valves produce the first heart sound?

The mitral and tricuspid valves, closing at the start of ventricular systole.

Which heart defect gives fixed splitting of S2?

Atrial septal defect: the shunt evens out filling of both ventricles in both phases of breathing.

Why is there no S4 in atrial fibrillation?

S4 depends on an effective atrial contraction against a stiff ventricle, and in atrial fibrillation there is none.

What does an S3 suggest in a breathless 65-year-old?

Heart failure with a dilated or volume-overloaded ventricle.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

← All of the clinical exam

Educational content on the clinical exam; it is learned and practised under supervision. It does not replace assessment by a health professional and is not for self-diagnosis.

Sources: 19.3 Cardiac Cycle - Anatomy and Physiology 2e | OpenStax (OpenStax (Rice University), 2022); 24.3 Nursing Assessment - Clinical Nursing Skills | OpenStax (OpenStax (Rice University), 2024); Mitral stenosis: MedlinePlus Medical Encyclopedia (MedlinePlus, U.S. National Library of Medicine, 2026).

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Representative model, for educational purposes only.