A Guide To The Heart Sounds

SECOND HEART SOUND (S2)

What Is It?

The second heart sound (S2) refers to one that is normal and present in most all individuals. It produces a rhythm characterized as sounding like “lub-DUB” (with S1 being the first syllable, and S2 being the second syllable). 

What Causes It?

It is believed that the closing of the aortic and pulmonary valves is what is responsible for the S2 heart sound. These components of the S2 sound can be referred to as A2 and P2 respectively. 

THIRD HEART SOUND (S3)

What Is It?

The third heart sound (S3) refers to a heart sound that is sometimes abnormal and not present in everyone (can be present in some young individuals and well-trained athletes. It produces a rhythm described as sounding like “ken-tuc-KY” (S1 being the first syllable, S2 the second, and S3 the third).

What Causes It?

This heart sound is believed to result from when the inflow from the left atrium strikes blood that is already present in the left ventricle (causing reverberations of blood along the walls of the left ventricle). It can be present in the setting of: 

  • Left ventricular failure
FOURTH HEART SOUND (S4)

What Is It?

The fourth heart sound (S4) refers to a heart sound that is abnormal and not present in everyone. It produces a rhythm described as sounding like “TEN-nes-see” (with S4 being the first syllable, S1 the second, and S2 the third).

What Causes It?

S4 corresponds in timing with atrial contraction, and is thought to be causes by the sound of blood striking a stiffened left ventricle. Causes of a stiffened left ventricle can include:

  • Restrictive cardiomyopathy
  • Left ventricular hypertrophy from prolonged hypertension.