10.8: Heart Sounds
- Page ID
- 100127
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The two major heart sounds are “lub” (from the closure of AV valves) and “dub: (from the closure of aortic and pulmonary valves).
- Describe how normal heart sounds (S₁ and S₂) are produced and what valve events correspond to each.
- Explain heart murmur as a common abnormal heart sound and explain what it indicates about cardiac function.
Listening to the heart is a simple, inexpensive, and informative way to assess cardiac function. Unlike the ECG, which records the heart’s electrical activity, this test relies on sound. You have already learned about the familiar “lub-dub” rhythm heard through a stethoscope. These sounds are not produced by the actual contractions of the heart but by the closing of its valves, which create vibrations in the blood and surrounding heart tissues.
Listening to heart sounds, a process called auscultation, allows clinicians to assess how effectively the valves are opening and closing and to detect abnormalities such as murmurs that may indicate turbulent blood flow or valve disease.
S1
The first heart sound, S₁ (“lub”), occurs when the atrioventricular (AV) valves — the tricuspid and mitral valves — close following ventricular systole at the start of ventricular systole (contraction). There is a very slight split between the closure of the mitral and tricuspid valves, but it is not long enough to create multiple sounds.
S2
The second heart sound, S₂ (“dub”), follows when the semilunar valves — the aortic and pulmonary valves — close as the ventricles relax at the beginning of diastole, following ventricular systole. S2 is split because aortic valve closure occurs before pulmonary valve closure. During inspiration (breathing in) there is slightly increased blood return to the right side of the heart, which causes the pulmonary valve to stay open slightly longer than the aortic valve. Due to this, the naming convention is to divide the second sound into two second sounds, A2 (aortic), and P2 (pulmonary). The time between A2 and P2 is variable depending on the respiratory rate, but the split is generally only prominent in children during inspiration. In adults and during expiration, the split is usually not long enough to suggest two sounds.
Abnormal Heart Sounds
Abnormal heart sounds arise when normal cardiac flow or function is disrupted. Heart murmurs are the most common example, produced by turbulent blood flow through the heart or its valves. This turbulence often results from valve abnormalities:
- If a valve fails to close completely, blood leaks backward in a condition called regurgitation.
- If it does not open fully, the narrowing is termed stenosis.
Murmurs have a characteristic “whooshing” or “slosh” quality and are classified by their intensity (graded 1–6), pitch, configuration, location, and timing within the cardiac cycle.
Other abnormal heart sounds, such as S3 and S4, are not caused by valve defects but by abnormal ventricular mechanics. An S3 sound occurs just after the normal “lub-dub” and is linked to rapid ventricular filling in an overly compliant or weakened ventricle, often seen in heart failure. An S4 sound occurs just before the “lub-dub” and results from forceful atrial contraction into a stiff or hypertrophied ventricle. These extra sounds generally indicate more significant cardiac dysfunction than typical murmurs.
