Auscultation of Cardiac Heart Sounds (S3,S4)


LSU Physician Champion - Dr. David Tadin


Dorsalis Pedis Pulse


Sometimes an S3 or S4 can be heard. The S3 is a dull, low-pitched sound best heard over the cardiac apex (needs to locate the point of maximum impulse (PMI)) with the patient lying in the left lateral decubitus position with the bell of the stethoscope. It occurs at the beginning of the middle third of diastole, approximately 0.12 to 0.18 seconds after S2 (See figure 3). This produces a rhythm classically compared word "Kentucky" with Ken(S1)tucky(S2-S3). An S3 may be normal in people under 40 years of age, pregnancy and some trained athletes but should disappear before middle age. A pathologic S3 occurs from high left sided filling pressures in which blood from the left atrium during passive filling is rapid and decelerates into wall the left ventricle causing vibratory oscillations. An S3 can be heard over the right ventricle as well. The S4 is a low-pitched sound that results from a forceful atrial kick at the end of diastole during into a ventricle which cannot expand further. S4 occurs ~90 msec before S1 (See figure 3). This sound is best heard over the cardiac apex (needs to locate the point of maximum impulse (PMI)) with the patient lying in the left lateral decubitus position with the bell of the stethoscope. It will become more apparent with exercise or with the patient holding expiration. If the culprit is the right ventricle, the abnormal sound will be most evident on the left lower border of the sternum and will get louder with exercise and deep inspiration. This produces a rhythm classically compared word "Tennessee" with Tennne(S4-S1)see(S2).


Figure 2 Normal sounds of the cardiac cycle.