Intro to Heart Sounds

The ability to detect abnormal heart sounds can give important information about the heart’s ability to function adequately. Normal individuals have at least two heart sounds – the first heart sound (S1) and the second heart sound (S2). Some individuals may also have a third heart sound (S3) and/or a fourth heart sound (S4). Closure of the mitral (and possibly also of the tricuspid) valve at the beginning of systole produces the S1. Closure of the aortic and pulmonic valves at the end of systole is responsible for the S2.

The S3 results from vigorous filling of the ventricle early in diastole. The S3 is a passive phenomenon in that its production does not require contraction of the muscle of any of the cardiac chambers. The S3 is present in many normal, asymptomatic individuals below the age of 40. However, in patients with symptoms consistent with HF, especially patients above the age of 40, the S3 is highly specific for HF.

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Location of Heart Sounds in the Cardiac Cycle	Listen to the S3 Heart Sound

According to an article published in the New England Journal of Medicine in 2001 by Drazner et al, the third heart sound is 99% specific for heart failure. Furthermore the study indicates patients with a third heart sound are at significantly greater risk for hospitalization, adverse outcomes, and death.

The S4 occurs as blood enters a relatively non-compliant ventricle late in diastole. Unlike the S3, the S4 is an active sound whose production requires forceful contraction of the atrial muscle.