Heart Sounds

When a stethoscope is placed over different regions of the heart, there are four basic heart sounds that can be heard (listening to heart sounds is called cardiac auscultation). The sounds waves responsible for heart sounds (including abnormal sounds such as murmurs) are generated by vibrations induced by valve closure, abnormal valve opening, vibrations in the ventricular chambers, tensing of the chordae tendineae, and by turbulent or abnormal blood flow across valves or between cardiac chambers (see heart anatomy).

The most fundamental heart sounds are the first and second sounds, usually abbreviated as S₁ and S₂. S₁ is caused by closure of the mitral and tricuspid valves at the beginning of isovolumetric ventricular contraction. S₁ is normally slightly split (~0.04 sec) because mitral valve closure precedes tricuspid valve closure; however, this very short time interval cannot normally be heard with a stethoscope so only a single sound is perceived. S₂ is caused by closure of the aortic and pulmonic valves at the beginning of isovolumetric ventricular relaxation. S₂ is physiologically split because aortic valve closure normally precedes pulmonic valve closure. This splitting is not of fixed duration. S₂ splitting changes depending on respiration, body posture and certain pathological conditions.

The third heart sound (S₃), when audible, occurs early in ventricular filling, and may represent tensing of the chordae tendineae and the atrioventricular ring, which is the connective tissue supporting the AV valve leaflets. This sound is normal in children, but when heard in adults it is often associated with ventricular dilation as occurs in systolic ventricular failure.

The fourth heart sound (S₄₎, when audible, is caused by vibration of the ventricular wall during atrial contraction. This sound is usually associated with a stiffened ventricle (low ventricular compliance), and therefore is heard in patients with ventricular hypertrophy, myocardial ischemia, or in older adults.

Heart Sound	Occurs during:	Associated with:
S1	Isovolumetric contraction	Closure of mitral and tricuspid valves
S2	Isovolumetric relaxation	Closure of aortic and pulmonic valves
S3	Early ventricular filling	Normal in children; in adults, associated with ventricular dilation (e.g. ventricular systolic failure)
S4	Atrial contraction	Associated with stiff, low compliant ventricle (e.g., ventricular hypertrophy

In addition to these four basic heart sounds, other sounds such as murmurs can be heard. To learn more about these, click here.

An excellent resource for listening to the heart sounds can be found at:
http://www.cardiosource.com/heartsounds/index.asp#

Revised 04/05/07