CorpusHuman Anatomy
CardiovascularPhysiological process

Heart sounds and murmurs

Also known as: S1, S2, S3, S4, murmurs, auscultation

Heart sounds are vibrations heard through a stethoscope, produced mainly by valve closure. S1 comes from closure of the AV valves and S2 from closure of the semilunar valves. S3 and S4 are extra sounds that may be normal or pathological. Murmurs are produced by turbulent blood flow.

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Overview

S1 ("lub"). Closure of the mitral valve (M1), followed by the tricuspid valve (T1). It marks the start of systole and is loudest at the apex. S1 is loud in mitral stenosis, with a short PR interval and in hyperdynamic states. It is soft in mitral regurgitation, with a long PR interval and in severe heart failure.

S2 ("dub"). Closure of the aortic valve (A2), followed by the pulmonary valve (P2). On inspiration, more blood returns to the right heart, so right ventricular ejection lasts longer and P2 comes later. At the same time A2 comes slightly earlier. The result is physiological splitting of S2 on inspiration.

Abnormal splitting has typical causes. Wide splitting that still varies with breathing occurs in RBBB and pulmonary stenosis. Fixed splitting occurs in an atrial septal defect. Reversed (paradoxical) splitting, with P2 before A2, occurs in LBBB and severe aortic stenosis. A loud P2 suggests pulmonary hypertension.

S3 is a low-pitched sound in early diastole, caused by rapid filling of the ventricle (rhythm like "Ken-tuc-ky"). It is normal in children, young adults, athletes and pregnancy. In older adults it suggests heart failure or volume overload, for example from mitral regurgitation.

S4 comes in late diastole, when the atria contract against a stiff ventricle (rhythm like "Ten-nes-see"). It occurs in LVH, hypertension, HCM and acute ischaemia. It can never be heard in atrial fibrillation, because there is no effective atrial contraction.

Other sounds. These include the opening snap of mitral stenosis, the ejection click of a bicuspid aortic valve or pulmonary stenosis, the mid-systolic click of mitral valve prolapse, the pericardial friction rub and the pericardial knock.

Parts & subdivisions

  1. Aortic area
    2nd right intercostal space at the sternal border.
  2. Pulmonary area
    2nd left intercostal space at the sternal border.
  3. Erb's point
    3rd left intercostal space at the sternal border. Aortic regurgitation is often best heard here.
  4. Tricuspid area
    4th–5th left intercostal space at the lower sternal edge.
  5. Mitral area (apex)
    5th left intercostal space in the midclavicular line.

Function

  • Allow valve function, cardiac timing and the presence of shunts or turbulence to be assessed at the bedside.
Physiology

Murmurs. Murmurs are caused by turbulence, which occurs when flow is fast, the opening is narrow or the blood is thin (low viscosity). They are graded from 1 to 6 (Levine scale); grade 4 or above has a palpable thrill.

By timing, murmurs fall into four groups. Ejection systolic murmurs occur in aortic stenosis, pulmonary stenosis, HCM and high-flow states. Pansystolic murmurs occur in mitral regurgitation, tricuspid regurgitation and VSD. Early diastolic murmurs occur in aortic and pulmonary regurgitation. Mid-diastolic murmurs occur in mitral and tricuspid stenosis. A continuous murmur is typical of a PDA.

Manoeuvres change murmurs in predictable ways. Inspiration makes right-sided murmurs louder. A Valsalva manoeuvre or standing up reduces venous return and softens most murmurs, but makes the murmurs of HCM and mitral valve prolapse louder. Squatting and sustained handgrip increase afterload, which makes the murmurs of AR, MR and VSD louder and the murmur of HCM softer.

Clinical significance

Innocent (flow) murmurs

Innocent murmurs are common in children, in pregnancy, in anaemia and with fever. They are soft (grade 2 or less), ejection systolic and have no thrill. The heart sounds are normal and the patient has no symptoms.

Mnemonics

Auscultation areas

"All Physicians Take Money": Aortic, Pulmonary, Tricuspid, Mitral.

Which side gets louder

RILE: Right-sided murmurs get louder on Inspiration, Left-sided murmurs on Expiration.

Systolic vs diastolic lesions

"MR. ASS": Mitral Regurgitation and Aortic Stenosis are Systolic. "MS. ARD": Mitral Stenosis and Aortic Regurgitation are Diastolic.

Compiled from standard anatomy and physiology references — see the Cardiovascular System sources. For education only; not medical advice.