Heart Sounds and Murmurs

Heart sounds are the audible vibrations produced by the mechanical events of the cardiac cycle - chiefly the closure of the heart valves - while murmurs are the more prolonged sounds generated by turbulent blood flow. Listening to them (auscultation) is a window onto cardiac mechanics, letting an examiner infer the timing of valve events and the presence of abnormal flow.

Definition

Heart sounds are transient vibrations created by valve closure and associated cardiac events during the cardiac cycle, and murmurs are sustained sounds produced by turbulent blood flow across valves or through abnormal channels.

Scope

The topic covers the origin and timing of the normal heart sounds (S1 and S2, and the added sounds S3 and S4), the genesis of murmurs from turbulent flow, and the relationship of these acoustic events to the underlying cardiac cycle. It is a physiological account of how the sounds arise and what they signify, not a manual for diagnosis.

Core questions

• What produces the first and second heart sounds?
• What do the third and fourth heart sounds represent?
• How are the heart sounds timed within the cardiac cycle?
• How does turbulent flow generate a murmur?
• How do timing and location help characterise a murmur's origin?

Key concepts

• First heart sound (S1) from mitral and tricuspid closure
• Second heart sound (S2) from aortic and pulmonary closure
• Physiological splitting of S2
• Third and fourth heart sounds (S3, S4)
• Turbulent flow and the genesis of murmurs
• Systolic versus diastolic timing of murmurs

Mechanisms

The mechanical events of the cardiac cycle set up vibrations heard at the chest wall. The first heart sound (S1) marks the onset of systole and arises chiefly from closure of the mitral and tricuspid valves, while the second sound (S2) marks the end of systole and arises from closure of the aortic and pulmonary valves; the slight asynchrony of aortic and pulmonary closure produces the physiological splitting of S2, as described in standard physiology texts. Added low-frequency sounds - S3 in early diastole and S4 in late diastole - reflect rapid ventricular filling and atrial contraction against a stiff ventricle. Murmurs arise when blood flow becomes turbulent, for example crossing a narrowed or leaking valve; their timing within systole or diastole and their location point to the responsible structure, as reviewed in the auscultation literature, although imaging such as echocardiography is now used to confirm and quantify the underlying lesion.

Clinical relevance

Auscultation of heart sounds and murmurs is a long-standing bedside method for detecting valvular and structural heart disease, and the acoustic findings are interpreted alongside echocardiography for confirmation. This entry explains the physiological origin and timing of the sounds for reference and is not a basis for individual diagnosis or treatment decisions.

Evidence & guidelines

The genesis and timing of heart sounds are described in standard physiology and cardiology textbooks (Guyton and Hall; Braunwald), the clinical interpretation of valvular auscultation in review articles (Hall, 2018), and the imaging that now complements auscultation in consensus recommendations (Lang, 2015).

History

Cardiac auscultation became a systematic clinical method after Rene Laennec introduced the stethoscope in the early nineteenth century, and the correlation of specific sounds and murmurs with valve events and lesions was refined across the nineteenth and twentieth centuries. With the advent of echocardiography, auscultation shifted from a primarily diagnostic tool to a screening and teaching skill complemented by imaging.

Key figures

• Rene Laennec
• Eugene Braunwald

Seminal works

• hall-bjca-2018
• lang-2015

Frequently asked questions

What causes the 'lub-dub' of the heartbeat?

The 'lub' is the first heart sound (S1), produced as the mitral and tricuspid valves close at the start of systole, and the 'dub' is the second heart sound (S2), produced as the aortic and pulmonary valves close at the end of systole.

What is the difference between a heart sound and a murmur?

Heart sounds are brief vibrations from discrete events such as valve closure, whereas a murmur is a longer, whooshing sound caused by turbulent blood flow, for example across a narrowed or leaking valve.