Fourth Heart Sound

The fourth heart sound (S4) is very quiet, and is not usually heard with a normal, unamplified stethoscope.  When present, it occurs in late diastole and coincides with the contraction of the atria.  It is generated by the left (or right) atrium contracting against a stiffened ventricle.  Because of this, the presence of a fourth heart sound usually indicates the presence of a cardiac disease - specifically a decrease in ventricular compliance.  This is usually due to ventricular hypertrophy or myocardial ischaemia.

The S4 is a dull, low-pitched sound (like S3), and is best heard in the mitral area.

An S4 is sometimes referred to as an atrial "gallop".

 

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