Third Sound

The next extremely important finding we must learn together is the third heart sound. In my opinion, all sounds and murmurs are not created equal, including the “Big 12.” Filling sounds are extremely important and the third heart sound is an example of a filling sound. Now, we are going to continue to examine this normal patient, although a third heart sound can also clearly be abnormal. But, let’s listen at the apex in this normal patient and, critically important also, you listen with the bell so that you enhance the low-frequency sounds, and you bring it out and you can readily hear it. And in your patient, you may want to lay them over in the left lateral decubitus position to hear it, as the heart comes closer to the chest wall. Let’s use the carotid vessel for timing and everyone listen together. [sounds]
And what did we hear in this normal patient? We heard lup dub pum, lup dub pum, lup dub pum. You do that, mimic it, lup dub pum, lup dub pum. Very, very important finding that’s a third heart sound and, in this case, in the normal patient, it is due to the fact that blood goes rushing and accelerating into the ventricle in early diastole and then decelerates normally, but that sets up vibrations in the normal patient. But it could be found in a patient with a stiff, poorly compliant ventricle when the deceleration is enhanced, so that blood goes into the ventricle, decelerates more rapidly and you hear the same thing lup dub pum, lup dub pum, lup dub pum, lup dub pum. It is a bedside reflection of ventricular function in that case, and it is an extremely important finding.

Third Heart Sound

Third heart sounds are early diastolic, low-frequency filling sounds, best heard with the bell of the stethoscope. They occur approximately fifteen hundredths of a second after the second sound, and are related to the acceleration and deceleration of blood during early, passive filling of the ventricle. Left ventricular third sounds may be heard in many normal children and young adults, as blood rapidly accelerates into the ventricle. They may also be pathologic in heart failure, as blood rapidly decelerates due to a less compliant ventricle. Left ventriclar third sounds are best heard at the apex. Right ventricular third sounds are best heard at the tricuspid area and may augment with inspiration.

S3 Heart Animation

This is a graphic example of the heart in a normal patient with a third heart sound at the apex. In the animation that follows, we can appreciate that the third heart sound is generated during early diastole, and it is associated with rapid ventricular filling.

Pressure curve - Filling Sound S3

This is a graphic example of an S1 and an S2 followed by an S3. By simultaneosly viewing the ventricular volume curve, one can appreciate that the third sound occurs just at the end of early rapid diastolic filling. Let us listen together.