THIRD HEART SOUND
The S3 (ventricular gallop) occurs in early diastole, 130 to 180 msec after A2, and coincides with the end of rapid filling of the left ventricle (LV). Ultrasonic studies have shown that the S3 occurs just as the LV septum and posterior free wall reach their greatest diastolic excursion; presumably, accelerating and decelerating forces are maximal at this time. The sound itself thus represents vibrations of LV structures and blood mass as the rapid inflow of left atrial blood is checked by the limits of LV diastolic expansion.
Implications of an Audible S3
The presence of an audible S3 is normal in children and young adults. For unclear reasons, the S3 is rarely a normal finding in persons more than 30 to 35 years of age. It has been recognized for many years that the presence of a S3 in an adult generally has ominous implications. An
Abrams J. Current Concepts of the Genesis of Heart Sounds: II. Third and Fourth Sounds. JAMA. 1978;239(26):2790–2791. doi:10.1001/jama.1978.03280530054029
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