Heart Sounds

Heart sounds are brief, transient sounds produced by valve opening and closure and by movement of blood in the heart. They are divided into systolic and diastolic sounds. In most cases, only the first (S1) and second (S2) heart sounds are heard. These are high-frequency sounds and arise from aortic and pulmonary valve closure (S1), as well as mitral and tricuspid valve closure (S2).  The third heart sound (S3) may be physiologic (e.g., athletes) or pathologic (e.g., congestive heart failure), and is related to abnormally rapid deceleration of early diastolic left ventricular inflow. The fourth heart sound (S4) is associated with contraction of the atria into partially-filled and non-compliant (stiff) ventricles. S4 is a pathologic sign in the young, but may be found in older individuals due to an age-related decrease in ventricular compliance. Additional sounds include murmurs (physiologic and pathologic), clicks, and snaps. These sounds are heard in individuals with structural abnormalities of the heart such as septal defects, valvular stenosis, and mitral regurgitation.

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Overview

Heart sounds

  • Heart sounds are produced by:
    • Valve opening and closure
    • Movement of blood in the heart
  • The more turbulent the flow, the more audible the created vibrations.
  • On auscultation, 2 heart sounds heard from a normal heart are reflective of the cardiac cycle.
    • The cardiac cycle is a sequence of pressure changes in the heart, resulting in:
      • Systole (ventricular contraction and ejection of blood) and
      • Diastole (ventricular relaxation and filling)
    • S1 and S2 mark the beginning and end, respectively, of the cardiac cycle phases: systole and diastole; they are high-frequency sounds.
    • Colloquially referred to as the “lub-dub” sound of the heart
  • S3 and S4 are low-frequency sounds which may be heard in various conditions.
Table: Heart sounds
SoundTimingAssociation
S1 Isovolumetric contraction (beginning of systole) Closure of atrioventricular valves
S2 Isovolumetric relaxation (beginning of diastole) Closure of semilunar valves
S3 Rapid filling of ventricles (early diastole)
  • Normal in pregnant women, children, athletes
  • Ventricular dilation (e.g., congestive heart failure)
S4 Late filling of ventricles by atrial contraction (late diastole)
  • Noncompliant or stiff ventricles
  • Pathologic in children and young people
  • May be seen in older people with age-related stiff ventricles

S1 and S2

S1

  • Closure of the atrioventricular (AV) valves
  • Mitral valve (M1) closes before the tricuspid valve (T1).
  • Indicates the start of systole
  • Coincides with the QRS complex and isovolumetric contraction (beginning of systole)
  • Loudest over the mitral area (cardiac apex)
S1

S1:
Closure of the atrioventricular valves (tricuspid and mitral) at the beginning of systole. In the systole phase of the cardiac cycle, the right and left ventricles develop pressure, leading to ventricular contraction and ejection of blood into the pulmonary artery and aorta, respectively. Thus, the pulmonary and aortic valves are open. The closed atrioventricular valves prevent the backflow of blood into the atria during ventricular contraction.

Image: “2013 Blood Flow Contracted Ventricles” by OpenStax College. License: CC BY 3.0

S2

  • Closure of the semilunar valves (pulmonary and aortic)
  • Indicates the start of diastole
  • Occurs just after the T-wave and coincides with isovolumetric relaxation (beginning of diastole)
  • The aortic valve (A2 component of S2) closes before the pulmonic valve (P2 component of S2).
  • Loudest at left upper sternal border

Audio:

Normal S1 and S2: In this audio clip, normal S1 and S2 heart sounds can be heard. S1 corresponds to the closure of the AV valves, marking the beginning of systole. S2 corresponds to the closure of the semilunar valves, marking the beginning of diastole.

Heart sound by The Regents of the University of Michigan. License: CC BY-SA 3.0

Related videos

S3 and S4

S3 and S4 sounds are heard in certain clinical situations and are produced by turbulent blood entering the ventricle at different points during diastole. S3 and S4 are the so-called “extra heart sounds.” They are low-frequency sounds.

S3

  • Rapid filling phase of ventricular diastole
  • ↑ Left ventricular filling pressure → ↑ cardiac output
  • Best heard at the apex (left lateral decubitus position)
  • Can be normal in children, pregnant women, and athletes
  • Associated pathologic conditions:
    • Dilated cardiomyopathy
    • Congestive heart failure
    • Chronic mitral regurgitation (MR)
    • Chronic aortic regurgitation (AR)
    • Thyrotoxicosis
Timing and amplitude of S3

Timing and amplitude of S3 when inaudible and audible

Image by Lecturio.

Audio:

S3: In this audio clip, the S3 gallop can be heard (left decubitus, heard with the bell of the stethoscope). S3 occurs after S2 during the rapid filling phase of ventricular diastole.

Heart sound by The Regents of the University of Michigan. License: CC BY-SA 3.0

S4

  • Atrial contraction or “kick” during ventricular diastole
  • Due to ventricular noncompliance or stiffness
  • May be auscultated in older adults due to loss of ventricular compliance with age
  • Best heard at the apex (left lateral decubitus position)
  • Associated conditions:
    • Hypertrophic cardiomyopathy
    • AS
Timing and amplitude of S4

Timing and amplitude of S4 when inaudible and audible

Image by Lecturio.

Audio:

S4 gallop: In this audio clip, the S4 gallop can be heard (left decubitus, heard with the bell of the stethoscope). S4 occurs before S1 during the atrial filling phase. S4 is heard in conditions where there is stiffness or low compliance in the ventricle.

Heart sound by The Regents of the University of Michigan. License: CC BY-SA 3.0

Related videos

Respiratory Variation

An increase in right ventricular (RV) volume (occurring with inspiration) affects the right side of the heart and is heard as splitting of S2 (A2 and P2).

Physiologic splitting

  • Associated condition: inspiration
  • In inspiration:
    • ↑ Venous return, ↑ RV filling and volume 
    • Delays closure of pulmonic valve → delays P2
Widening of the components of S2

Diagram showing widening of the S2 components (A2 and P2) during increased preload conditions such as inspiration, which produces the physiologic splitting of S2

Image by Lecturio.

Widened or persistent splitting

  • Description:
    • Delayed RV emptying → delayed pulmonic sound (exaggeration of normal splitting)
    • Varies with inspiration
  • Associated conditions:
    • Pulmonic stenosis (PS)
    • Right bundle branch block
Persistent splitting of S2

Diagram showing persistent S2 splitting in which closure of the pulmonic valve is further delayed by inspiration (right). This splitting can occur in a right bundle branch block.

Image by Lecturio.

Audio:

Persistent S2 splitting: heard in right bundle branch block (listening with the diaphragm of the stethoscope)

Heart sound by The Regents of the University of Michigan. License: CC BY-SA 3.0

Fixed splitting

  • Description:
    • ↑ Right atrial (RA) and RV volume (due to left-to-right shunt)
    • ↑ Blood flow through the pulmonic valve
    • Delays closure of the pulmonic valve
  • Associated condition: atrial septal defect (ASD)
Fixed splitting

Diagram showing fixed splitting, in which closure of P2 is NOT delayed by inspiration (right)

Image by Lecturio.

Paradoxical splitting

  • Description:
    • Delayed aortic valve closure
    • Pulmonic valve closure (P2) occurs before delayed aortic valve closure (A2).
  • Associated conditions:
    • Delayed aortic valve closure due to obstruction:
      • Aortic stenosis (AS)
      • Hypertrophic obstructive cardiomyopathy (HOCM)
    • Delayed aortic valve closure due to conduction disease: left bundle branch block
Paradoxical splitting of S2

Diagram showing paradoxical splitting in which closure of the aortic valve is delayed: The name “paradoxical” is because the split narrows the inspiration (right). The split can be heard in some individuals with a left bundle branch block.

Image by Lecturio.

Clicks and Snaps

Clicks

  • A high-pitched sound occurring at the point of maximal opening of the valves
  • Occurs after S1 (systolic)
  • Can be ejection or nonejection clicks:
    • Ejection clicks:
      • Aortic or pulmonary in etiology
      • Heard in early systole, indicating the rapid opening of a semilunar valve or distention of the aorta during the beginning of ventricular ejection
    • Nonejection click: 
      • Mitral or tricuspid in etiology
      • Usually mid-to-late systolic: swelling out and sudden stop of the leaflets of a prolapsed mitral valve
Diagram depicting the the mid-systolic click

Schematic diagram depicting the mid-systolic click (MSC): MSC occurs after S1.

Image by Lecturio.

Audio:

Mid-systolic click (MSC): This audio clip is an example of an MSC heard in mitral valve prolapse. An MSC is a crisp sound occurring between S1 and S2 (no murmur follows).

Heart sound by The Regents of the University of Michigan. License: CC BY-SA 3.0

Snap

  • A high-frequency diastolic sound made by the opening of a stenotic mitral valve (most common)
  • Leaflets swell out into the ventricle and suddenly stop, producing a mid-to-high–frequency sound.
Diastolic filling and rumbling murmur of mild and severe mitral stenosis

Diastolic filling and rumbling murmur in mild and severe mitral stenosis:
The mid-diastolic murmur starts after the opening snap (O.S.). The presystolic murmur is due to atrial contraction (absent in atrial fibrillation) and is best heard over the apex with the bell of a stethoscope.

Image by Lecturio.

Audio:

Opening snap: A mitral stenosis murmur can be heard in this audio clip. The low-pitched, rumbling murmur starts after the opening snap of the mitral valve (after S2) and finishes with a short crescendo up to S1.

Heart sound by The Regents of the University of Michigan. License: CC BY-SA 3.0

Murmurs

Heart murmurs

  • Murmurs are audible vibrations that can be produced by the following:
    • Accelerated blood flow (e.g., increased preload)
    • Flow through a narrow opening (e.g., valvular stenosis)
    • Backward flow through an incompetent valve (e.g., valvular regurgitation)
  • Not all murmurs indicate structural heart disease.
  • Determine characteristics by:
    • Timing (cardiac cycle)
    • Intensity
    • Pattern or configuration
    • Pitch and quality
    • Location or auscultation area
    • Maneuvers, position, and exercise

Classification according to cardiac cycle

  • Systolic (occurs at or after S1 and ends before or at S2)
    • Early systolic: heard in acute mitral or tricuspid regurgitation (TR)
    • Midsystolic: aortic or pulmonary stenosis
    • Holosystolic:
      • Mitral or TR
      • Ventricular septal defect (VSD)
    • Late systolic: mitral valve prolapse
  • Diastolic (occurs at or after S2 and ends before or at S1)
    • Early diastolic: aortic or pulmonary regurgitation
    • Mid diastolic: mitral stenosis, tricuspid stenosis (TS)
    • Late diastolic (or presystolic):
      • Moderate-to-severe AR (Austin Flint murmur)
      • Mitral stenosis
  • Continuous (not confined to either systole or diastole):
    • Patent ductus arteriosus murmur
    • Arteriovenous fistulas
Patterns of heart murmurs

Patterns of heart murmurs (with examples):
A: presystolic or late diastolic, crescendo murmur (tricuspid stenosis)
B: holosystolic murmur (mitral regurgitation)
C: midsystolic, crescendo-decrescendo murmur (aortic stenosis)
D: long systolic, crescendo-decrescendo murmur (pulmonic stenosis)
E: early diastolic, decrescendo murmur (aortic regurgitation)
F: mid-diastolic murmur (mitral stenosis)
G: short mid-diastolic murmur
H: continuous murmur (patent ductus arteriosus)

Image by Lecturio.
AR murmur simplification

Diastolic murmur: Chronic aortic regurgitation (AR) results in an early diastolic murmur (high pitched). The murmur becomes holodiastolic in severe AR.

Image by Lecturio.

Audio:

Early diastolic murmur: Aortic regurgitation, a high-pitched decrescendo murmur, can be heard in this audio clip.

Heart sound by The Regents of the University of Michigan. License: CC BY-SA 3.0
Holosystolic murmur

Holosystolic murmur: Chronic mitral regurgitation can be heard as a holosystolic murmur at the apex, radiating to the axilla.

Image by Lecturio.

Audio:

Holosystolic murmur: This audio clip presents an example of a holosystolic murmur from MR. The murmur results in a high-pitched “blowing” sound through the entirety of the systole.

Heart sound by The Regents of the University of Michigan. License: CC BY-SA 3.0

Classification according to intensity

Using the Levine system, murmurs can be graded on a scale from I to VI, which reflects the intensity of the murmur. 

  • I: very soft, may only be heard by experienced cardiologists
  • II: faint but readily audible
  • III: readily audible, louder than grade 2, no thrill
  • IV: loud and accompanied by a palpable thrill
  • V: loud enough to be heard with a stethoscope lightly touching the chest
  • VI: loud enough to be heard with a stethoscope off the chest

Classification according to pattern

  • Crescendo-decrescendo murmur:
    • Ascending then descending systolic ejection murmur
    • Diamond shaped
    • Example: AS
  • Crescendo:
    • Ascending intensity from faint to loud
    • Example: can be heard in mitral valve prolapse
  • Decrescendo:
    • Descending intensity from loud to faint
    • Example: AR
  • Uniform/plateau: mitral/TR murmur
Crescendo-decrescendo murmurs

Crescendo-decrescendo murmurs: ascending then descending systolic murmur (diamond shaped) heard in aortic stenosis

Image by Lecturio.

Audio:

Crescendo-decrescendo murmur: In this audio clip, the sound of severe AS, a harsh, crescendo-decrescendo murmur occurring between S1 and S2, can be heard. The S2 heart sound is inaudible due to the severity of AS.

Heart sound by The Regents of the University of Michigan. License: CC BY-SA 3.0

Classification according to pitch and quality

  • Pitch:
    • Frequency of the murmur
    • High pitch:
      • TR
      • MR
      • AR
    • Low pitch: mitral stenosis
  • Quality: can be blowing, harsh, rumbling, scratchy, vibratory, squeaky, or musical

Auscultation areas

The 5 areas of auscultation can be recalled using the mnemonic, “All People Enjoy Time Magazine.”

  1. Aortic area: right 2nd intercostal space adjacent to the sternum
    • AS
    • Aortic valve sclerosis
    • Systolic flow murmurs
  2. Pulmonic area: left 2nd intercostal space adjacent to the sternum
    • PS
    • Systolic flow murmurs
  3. Erb’s (auscultation) point (left sternal border): left 3rd intercostal space
    • Systolic murmurs: HOCM
    • Diastolic murmurs:
      • AR
      • Pulmonic regurgitation (PR)
  4. Tricuspid area: left 4th–5th intercostal space adjacent to the sternum
    • Systolic murmurs:
      • TR
      • VSD
    • Diastolic murmurs:
      • TS
      • ASD
  5. Mitral area (apex): left 4th intercostal space, midclavicular line
    • Systolic murmurs:
      • MR (holosystolic)
      • Mitral valve prolapse
    • Diastolic murmurs: mitral stenosis (MS)
Auscultation areas

Auscultation areas and associated murmurs that are heard: aortic, pulmonic, Erb’s point, tricuspid, and mitral areas (APETM)
TR: tricuspid regurgitation
VSD: ventricular septal defect
TS: tricuspid stenosis
ASD: atrial septal defect
MR: mitral regurgitation
MS: mitral stenosis

Image by Lecturio.

Dynamic Auscultation

Cardiac physiology and maneuvers

  • Preload:
    • Stretching of cardiac muscles prior to contraction (ventricular filling)
    • Preload: increase in venous return into the right ventricle and decrease in venous return to the left ventricle:
      • Deep inspiration
      • Supine position
      • Squatting (seen in tetralogy of Fallot)
      • Passive leg raise (increased venous return due to gravity)
    • ↓ Preload: decrease in venous return → ↓ LV volume
      • Valsalva maneuver (straining phase)
      • Abrupt standing
  • Afterload:
    • Effective pressure against which the heart ejects blood during ventricular contraction
    • ↑ Afterload: handgrip

Effects on the intensity of heart murmurs

  • Respiration ( preload):
    • Inspiration generally increases right-sided murmurs due to increased preload (on the right).
    • Inspiration generally decreases left-sided murmurs, but expiration increases left-sided murmurs.
  • While standing and with the Valsalva maneuver (↓ preload), most murmurs decrease, EXCEPT the following:
    • HOCM (becomes louder)
    • Mitral valve prolapse (becomes longer and louder)
  • While squatting and with passive leg raise (↑ preload), most murmurs become louder, EXCEPT:
    • HOCM (becomes softer)
    • Mitral valve prolapse (becomes shorter, except in severe MR)
  • With isotonic and isometric (sustained handgrip) exercise (↑ afterload), most murmurs increase, EXCEPT:
    • HOCM (decreases in intensity)
    • AS (decreases in intensity, helping to differentiate AS from MR)
Table: Maneuvers that change the intensity of murmurs
Physiologic changesManeuverMurmurs that increase with maneuverMurmurs that decrease with maneuver
Increased preload (on the right) Inspiration Most right-sided murmurs Most left-sided murmurs
Increased preload
  • Lying supine
  • Passive leg raise
  • Squatting
Most murmurs
  • HOCM
  • Mitral valve prolapse
Decreased preload
  • Valsalva (straining)
  • Abrupt standing
  • HOCM 
  • Mitral valve prolapse
Most murmurs
Increased afterload Handgrip Most murmurs, especially AR, MR, VSD
  • AS
  • HOCM
HOCM: hypertrophic obstructive cardiomyopathy
AS: aortic stenosis
AR: aortic regurgitation
MR: mitral regurgitation
VSD: ventricular septal defect

Mnemonics

  • rIght-sided murmurs: increase with Inspiration
  • lEft-sided murmurs: increase with Expiration

Specific Murmurs

The table below lists cardiac abnormalities with their corresponding murmurs.

Table: Systolic murmurs
TypeCardiac cyclePatternLocationAdditional description
Aortic stenosisSystolicCrescendo-decrescendo murmurRight 2nd ICS (aortic)
  • Paradoxical splitting of S2 (A2 decreased)
  • S4
Pulmonic stenosisSystolicCrescendo-decrescendo murmurLeft 2nd ICS (pulmonic)
  • Click often present
  • ↑ With inspiration
Mitral valve prolapseSystolicClick, crescendo into S2 (can vary with severity)Left 4th ICS (mitral)Mid-to-late systolic click
Mitral regurgitationSystolicUniform (holosystolic)Left 4th ICS (mitral)
  • Holosystolic,
high pitched
  • Radiates to axilla
Tricuspid regurgitationSystolicUniform (holosystolic)LLSB (tricuspid)
  • Holosystolic, high pitched
  • ↑ With inspiration
VSDSystolicUniform (holosystolic)LLSB (tricuspid)
Harsh, loud murmur
ICS: intercostal
LLSB: left lower sternal border
VSD: ventricular septal defect
Table: Systolic murmurs
TypeCardiac cyclePatternLocationAdditional description
AR Diastolic Decrescendo Erb’s point
  • S3 in acute AR
  • High pitched
Pulmonary regurgitation Diastolic Decrescendo Erb’s point ↑ With inspiration
Mitral stenosis Diastolic Opening snap followed by decrescendo-crescendo murmur Left 4th ICS (mitral)
  • Opening snap
  • Low-pitched, rumbling, mid-to-late diastolic murmur
Tricuspid stenosis Diastolic Frequently with MS (but softer and shorter than MS) LLSB (tricuspid)
  • Very rare
  • Low pitched
  • ↑ With inspiration
Patent ductus arteriosus Continuous Crescendo-decrescendo murmur Left 1st and 2nd ICS Continuous machinery-like murmur
AR: aortic regurgitation
ICS: intercostal
LLSB: left lower sternal border
MS: mitral stenosis

Mnemonics for valvular murmurs

  • Systolic murmurs: MR. PV TR-APS
    • MR (Mitral Regurgitation)
    • P (mitral valve Prolapse)
    • V (VSD)
    • TR (Tricuspid Regurgitation)
    • A (Aortic stenosis)
    • PS (Pulmonic Stenosis)
  • Diastolic murmurs: MS. PAR-TS
    • MS (Mitral Stenosis)
    • P (Pulmonary regurgitation)
    • AR (Aortic Regurgitation)
    • TS (Tricuspid Stenosis)

References

  1. Alpert, M.A. (1990). Systolic Murmurs. In Walker, H.K., et al. (Ed). Clinical Methods: The History, Physical, and Laboratory Examinations. (3rd ed.) https://www.ncbi.nlm.nih.gov/books/NBK345/
  2. Gersh, B. (2021). Physiologic and pharmacologic maneuvers in the differential diagnosis of heart murmurs and sounds. UpToDate. Retrieved Sept 4, 2021, from https://www.uptodate.com/contents/physiologic-and-pharmacologic-maneuvers-in-the-differential-diagnosis-of-heart-murmurs-and-sounds
  3. Gomella, L.G., Haist, S.A. (2007). History and physical examination. In Gomella, L.G., Haist, S.A. (Eds.), Clinician’s Pocket Reference: The Scut Monkey (11th ed.) https://accessmedicine.mhmedical.com/content.aspx?bookid=365&sectionid=43074910
  4. Jacobs, W.R. (1990). Ejection Clicks. In Walker, H.K., et al. (Ed.), Clinical Methods: The History, Physical, and Laboratory Examinations. (3rd ed.) https://www.ncbi.nlm.nih.gov/books/NBK347/
  5. McGee, S. (2018). Miscellaneous heart sounds. In S. McGee MD (Ed.), Evidence-based physical diagnosis (1st ed., pp. 355–360) http://dx.doi.org/10.1016/B978-0-323-39276-1.00042-1
  6. Meyer, T. (2021). Auscultation of cardiac murmurs. UpToDate. Retrieved Sept 5, 2021, from https://www.uptodate.com/contents/auscultation-of-cardiac-murmurs-in-adults#H2
  7. Mohrman, D.E., Heller, L.J. (2018). The heart pump. In Mohrman, D.E., Heller, L.J. (Eds.), Cardiovascular Physiology (9th ed.). accessmedicine.mhmedical.com/content.aspx?aid=1153946347
  8. O’Gara, P.T., Loscalzo, J. (2018). Approach to the patient with a heart murmur. In J.L. Jameson, et al. (Ed.), Harrison’s Principles of Internal Medicine (20th ed.). https://accessmedicine.mhmedical.com/content.aspx?bookid=2129&sectionid=192012631
  9. Williams, E.S. (1990). The Fourth Heart Sound. In Walker H.K., et al. (Ed.), Clinical Methods: The History, Physical, and Laboratory Examinations (3rd ed.) https://www.ncbi.nlm.nih.gov/books/NBK344/

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