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 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: