The heart sounds are the sounds (=noise) that the heart makes while it is beating. They can best be heard using a stethoscope with the diaphragm located on the skin of the chest in ‘front’ of the heart.
The first two sounds from the heart are the loudest: the closing of the valves causes these sounds.
The first heart sound is caused by the closure of the AV-valves (at the beginning of the systole).
The second heart sound is caused by the closure of the SL-valves (at the end of the systole).
If you listen carefully, you may also detect two more sounds: the 3rd and the 4th heart sound.
The third heart sound is caused by the flow of the blood during the rapid filling phase.
The fourth heart sound is caused by the flow of the blood during the active filling phase.
Both these two sounds are much softer that the first two sounds.
B. Cardiac Murmurs:
Murmurs are abnormal sounds, in this case originating from the heart (i.e. cardiac), and are often (but not always) caused by valve deficiencies.
There are two possible deficiencies of the valves:
a. valvular stenosis
b. valvular regurgitation
Valvular regurgitation is often also called valvular incompetence.
In the case of a valvular stenosis, the valves do not open properly. Then, the opening is smaller, and the blood rushing through the valves will cause more noise (= murmur).
In the case of a valvular regurgitation (or incompetence), the valves do not close properly. Therefore, when these valves should be closed, blood will leak (= regurgitate) through the valves, which also creates a murmur.
Depending upon a) the valve and b) the type of defect, a systolic or a diastolic murmur can occur.
For example; a mitral valve incompetence, will cause regurgitation when it should be closed, which is during cardiac systole and therefore will cause a systolic murmur.
A mitral stenosis on the other hand, which means it does not open properly, which should be the case during diastole, will then cause a diastolic murmur.
An aorta stenosis (does not open properly) will cause a murmur when blood should flow through it, which is during the ejection phase, and is therefore a systolic murmur.
Note, by the way, the diamond shape of this systolic murmur in the diagram, which is caused by the initial increase, followed by the subsequent decrease in the left ventricular pressure.
An aortic regurgitation occurs when the valves don’t close properly. This occurs of course during the diastole. This murmur indicates that blood is flowing from the aorta back into the left ventricle!
By the way, why are we only discussing the valves in the left heart and not those in the right heart?
12. Because the pressure differences in the right heart are much lower than in the left heart. Therefore, although these valves could also develop stenosis or incompetence, the blood flow is much lower, the murmur is much softer and often can not be detected with a stethoscope.
C. Some Additional Points:
So, when thinking of these cardiac murmurs, it is crucial to think of the phases of the heart.
So, if there is a mitral stenosis -> then not good opening during diastole -> so murmur during diastole
But if there is mitral incompetence -> poor closure of the mitral valve -> so then a murmur during systole.
You can apply the same reasoning for the aorta valves (with opposite results!).
By the way, these are not the only murmurs that can be detected, with a stethoscope, from the heart. The heart can also produce other types of murmurs but these will be discussed in another chapter (coming …).
By the way, it is understandable that the SL-valves, when they close, produce a heart sound (the 2nd sound). But the AV-valves are very weak and soft tissue; how come they make such a sound when they close?
Looking and listening to a parachute gives the answer! When somebody jumps from a flying plane with a parachute, after a few seconds, he (or she) will open his or her parachute.
As the air flows into the parachute, as you may know, suddenly, the ‘skin’ is filled with air and expands with a bang!
The same thing is happening with the AV-valves.
As the AV-valves start to close, blood will flow into the cusps of the valves and pushes the valves with a bang against each other. This is the first heart sound!