A third heart sound occurs early in diastole. In young people and athletes it is a normal phenomenon. In older individuals it indicates the presence of congestive heart failure.
The third heart sound is caused by a sudden deceleration of blood flow into the left ventricle from the left atrium. In the anatomy tab you will see a thin-walled, dilated left ventricle with generalized decreased vigor of contraction.
In the presence of a third heart sound (S3) the first heart sound is decreased in intensity while the second heart sound is increased in intensity.
The third heart sound is a low frequency sound best heard with the bell of the stethoscope pressed lightly on the skin of the chest.
After reviewing the sound, use the waveform and anatomy tabs for more information about this sound.