Third Heart Sound (S3)

Definition

S3 results from the impact of inflowing blood against a distended or incompliant ventricle in mid diastole. It is a low-frequency soundoccurring ~120-150 msec after S2.

Listening Areas

Heard with the stethoscope bell over the LV apex (usually 5LICS) or the RV apex (usually over 4LICS or LMPC).

Associated Conditions

• Normal: High Cardiac Output (Athletes, Pregnancy)
• Mitral regurgitation
• Hypertrophic Cardiomyopathy
• Ischemic Cardiomyopathy
• Constrictive Pericarditis (S3 as pericardial knock)
• Anemia
• Hyperthyroidism
• Myxoma (Tumor Plop)

See Also:

Extra sounds near S2

• Split Second Sound (Split S2)
• Opening Snap (OS)
• Early Diastolic Sound of Mitral Prolapse
  (this is not common)

Notes

S3 is sometimes referred to as a gallop sound.

S3 is felt on the ear drums as much as it is heard when listening with a stethoscope. Thebell of your stethoscope is necessary to hear an S3, lightly applied to the patient's skin. You will not hear an S3 with the diaphragm, and you may not hear it at all with a bad stethoscope.

To improve your chances of hearing an S3, roll the patient on his or her left side (the left lateral decubitus position) to swing the cardiac apex against the chest wall, bringing it closer to your stethoscope chest piece. A sarcastic mnemonic: to remember the timing of S1 S2 S3, mutter under your breath in weary frustration, "What the hell..." almost whispering the last word.

During ventricular filling, the quantity of the inflowing blood can be either absolutely or relatively excessive for the ventricle as the ventricle approaches its maximal volume.

Absolutely excessive (i.e., LV is not the culprit):

• Severe mitral regurgitation

Relatively excessive (LV with impaired filling):

• Dysfunctional left ventricle with low ejection fraction
• Restrictive cardiomyopathy
• Constrictive pericarditis