Heart Sounds

Heart Sounds

There are 4 heart sounds which can be heard normally.

First heart Sound (S1)

First heart sound (S1) is produced by closure of mitral and tricuspid valves. It marks the beginning of systole and coincides with the downslop of QRS complex of the ECG.

It is louder than normal with high cardiac output, excitement, fever, mitral stenosis or left to right shunting as in atrial septal defect or total anomalous pulmonary venous drainage.

Second Heart Sound (S2)

S2 is produced by aortic and pulmonic valve closure. Aortic (A2) closure occurs first, followed by the pulmonic valve closure (P2). Thus S2 is normally split, with aortic component earlier and louder (because of high aortic diastolic pressure) than pulmonary component. Since right atrial and right ventricular blood flow increases during inspiration, pulmonic valve closure is delayed during inspiration thus widening the splitting interval of S2.

1. S2: Split: wider interval during inspiration than expiration: normal
2. S2: Widely split and fixed : L-R atrial shunt.
3. S2: closely split loud P2: Elevated pulmonary arterial pressure.
4. S2: Widely split and low intensity: pulmonary valve stenosis.

Third Heart Sound (S3)

S3 occurs in diastole and is due to rapid ventricular filling. It is audible in normal children.

It is prominent when left ventricular filling volume is increased e.g. mitral regurgitation and left to right shunts at ventricular (VSD) or ductal level (PDA).

Fourth Heart Sound S4

Occurs in late diastole and coincides with P-R interval of the ECG. It is due to atrial contraction. A loud S4 is found in severe aortic stenosis, ventricular failure and restrictive cardiomyopathies.

Gallop Rhythms

Occur when 3rd or 4th heart sounds are so placed that the distance of S3 or S4 from 1st and second heart sounds is almost equal.

Left ventricular failure which can occur in acute myocarditis is associated with gallop thythm.