S1 and S2 Heart Sounds, Extra Heart Sounds

by | 26 Jan, 2021

Basics of Heart Sounds – S1 and S2 heart sounds

There are 2 main heart sounds that can be heard during auscultation: S1 and S2, also affectionately known as ‘lub’ and ‘dub’ respectively.

Normal heart sounds

The S1 and S2 heart sounds are part of the normal heart sounds. Source: University of Michigan Murmur library

S1 heart sound corresponds to the closing of the mitral and tricuspid valves during systole. During systole, ventricular pressure rises, leading to opening of the aortic and pulmonary valves as well as closure of the mitral and tricuspid valves.

S2 heart sound corresponds to the closing of the aortic and pulmonary valves at the beginning of diastole. S2 may be subdivided into aortic (A2) and pulmonary (P2) sounds as the aortic valve closes slightly before the pulmonary valve. The splitting between A2 and P2 can be exaggerated by inspiration, particularly in young individuals.

The pulse can be felt during systole between the S1 and S2 heart sounds. This is particularly important for differentiating between systolic and diastolic murmurs (covered separately here), as well as identifying any pathological heart sounds.

Pathological Extra Heart Sounds – Clicks, Snaps, S3/S4 heart sounds

Ejection systolic click


Ejection systolic click
Ejection systolic click in aortic stenosis and pulmonary stenosis

Ejection systolic click with ejection systolic murmur. Source: University of Michigan Murmur library

Mid-systolic click

Cause of mid-systolic click: Mitral valve prolapse

Midsystolic click
Mid-systolic click in mitral valve prolapse

Mid-systolic click. Source: University of Michigan Murmur library

Opening snap

Causes of opening snap:

Opening snap
Opening snap seen in mitral stenosis and tricuspid stenosis

Opening snap with mid-diastolic murmur. Source: University of Michigan Murmur library

S3 and S4 heart sounds

S3 and S4 are extra heart sounds arising after S2.

The S3 heart sound occurs during ventricular filling. It can be a normal finding in people aged 40 or under. Pathological causes are mostly related to heart failure and include:

  • Ischaemic heart disease
  • Dilated cardiomyopathy
  • Hypertrophic cardiomyopathy
  • Mitral regurgitation
S3 S4
Pathological S3 and S4 heart sounds

 S3 heart sound. Source: University of Michigan Murmur library

The S4 heart sound arises when the atria contract against a stiff ventricle (such as in states of ventricular hypertrophy). Causes include:

  • Hypertension
  • Pulmonary hypertension
  • Aortic stenosis
  • Hypertrophic cardiomyopathy

S4 heart sound. Source: University of Michigan Murmur library

Tumour plop

A rare diastolic heart sound classically associated with the movement of the tumour in atrial myxomas. 

Changes in Volume

The loudness of heart sounds can be altered by changes in the force of valve closure.

Loud S1 heart sound


Loud A2 heart sound

Cause: Systemic hypertension

Loud P heart sound


Pathological Changes in S2 heart sound splitting

Wide-splitting S2 heart sound – splitting increases with inspiration:

Wide splitting2
Wide-splitting of S2 heart sound. Splitting increases with inspiration.


Fixed splitting S2 heart sound – splitting not affected by breathing:

Fixed splitting2
Fixed splitting of S2 heart sound. Splitting is not affected by inspiration.

Cause: Atrial septal defect

Reversed splitting S2 heart sound ­– splitting decreases with inspiration (so much so that it can lead to P2 arising before A2):

Reversed splitting
Reversed splitting of S2 heart sound. Splitting decreases with inspiration (and can lead to P2 arising before A2).


1 Comment

  1. s10 pickup

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