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The first heart sound (S1) is heard as a firm but dull “lubb” sound. It consists of four components: a low-frequency, indistinct vibration caused by ventricular contraction; a louder sound of higher frequency caused by closure of the mitral and tricuspid valves; a vibration caused by opening of the semilunar valves and early ejection of blood from the ventricles; and a low-pitched vibration produced by rapid ejection.
The second heart sound (S2) is shorter and higher pitched than the first, is heard as a “dupp” and is produced by closure of the aortic and pulmonary valves.
The third heart sound (S3) is very faint and is caused by blood rushing into the ventricles. It can be heard in most normal persons between the ages of 10 and 20 years.
The fourth heart sound (S4) is rarely audible in a normal heart but can be demonstrated on graphic records. It is short and of low frequency and intensity, and is caused by atrial contraction. The vibrations arise from atrial muscle and from blood flow into, and distention of, the ventricles.
Heart Murmurs are sounds other than the normal heart sounds emanating from the heart region. They are often heard as blowing or hissing sounds as blood leaks back through diseased and malfunctioning valves or as blood is pushed through narrowed or stenotic valve orifices.
heart soundsThe sounds heard with a STETHOSCOPE applied over the heart. The most prominent sounds are caused by the closure of the heart valves. Heart abnormalities, especially valve disorders, cause additional sounds, called MURMURS. The timing and characteristics of these give much information about the state of the heart.
heart soundsThe two sounds heard on listening to the heart with a stethoscope (auscultation) during normal cardiac contraction. The first (heard best at the apex) is due to the closure of the two atrioventricular valves (mitral and tricuspid); the second (heard best at the base of the heart) marks the closure of the aortic and pulmonary valves. Two components of the second sound can be heard separately (split heart sound) as a normal feature. Additional heart sounds (third or fourth) may be a sign of cardiac disease. See also cardiac cycle.
heart sounds; HS sounds (audible via a stethoscope) due to heart action
first HS caused by atrioventricular valve closure (occurs with ventricular systole)
second HS caused by semilunar valve closure (signifies beginning of diastole)
third HS corresponds to ventricular filling (occurs early in diastole)
fourth HS corresponds to atrial contraction (occurs late in diastole)