Heart Sounds and Valve Closures during Cardiac Cycle
During the cardiac cycle, there are two distinct heart sounds that can be heard through a stethoscope. These sounds are caused by the closing of the heart valves.
- First Heart Sound (S1)
The first heart sound (S1) is the loudest and is heard at the beginning of the cardiac cycle. S1 is caused by the closure of the tricuspid and mitral valves (also known as the atrioventricular valves) as the ventricles contract and fill with blood.
- Second Heart Sound (S2)
The second heart sound (S2) is softer than S1 and is heard at the end of the cardiac cycle. S2 is caused by the closure of the aortic and pulmonic valves (also known as the semilunar valves) as the ventricles relax and the blood flows back into the aorta and pulmonary artery.
- Additional Heart Sounds
In addition to S1 and S2, there may be additional heart sounds heard in some individuals. These include:
- Third Heart Sound (S3): a soft, low-pitched sound heard during early diastole, caused by the rapid filling of the ventricles with blood.
- Fourth Heart Sound (S4): a soft, low-pitched sound heard during late diastole, caused by atrial contraction and the filling of the ventricles.
It is important to note that the presence of S3 or S4 may indicate an underlying cardiac condition.
In summary, during the cardiac cycle, the closing of the heart valves produces two distinct heart sounds, S1 and S2. Additional heart sounds, such as S3 and S4, may also be present and may indicate an underlying cardiac condition.
