Updated: Nov 19, 2020
Everybody is acquainted with familiar “lub-dub” of the heart sounds, sometimes heard without any aid, but mostly if listened by the stethoscope or putting an ear to one’s chest. Every wonder how they are produced?
Well you be astonished, if I tell you that functionally we have 2-hearts, right and the left, connected to the vascular circuit in series.
The right heart consists of a right atrium, collecting deoxygenated blood from all parts of the body, except the lungs, and pouring this blood through a right atrioventricular opening into the right ventricle, which then pumps this deoxygenated blood to the lungs through an opening, called a pulmonary opening, into the pulmonary artery.
Likewise, the left heart consists of the left atrium, collecting oxygenated blood from the lungs and pouring through a left atrioventricular opening into the left ventricle, which then pumps the oxygenated blood to all parts of the body, except the lungs, through an opening called an aortic opening, into the aorta.
I am trying not to get too technical and use simple English to make you understand.
The blood flows through the two atrioventricular openings towards ventricles. When the ventricles contract, the blood should go into the large arteries openings, but it can also go back to the atria, can it? Yes, it can, but then both of these openings have got valves to protect the backward flow from the ventricles into the atria. On the left side, this valve is called Mitral and the right one is called a Tricuspid valve.
When the ventricles contract, these two valves shut the opening with a thug and it is this “thug” which is heard as “lub” and is known as the first heart sound. So the sound is not produced by the muscles contracting or the blood flow, but the closure of the valves, in this case, the mitral and tricuspid producing the first heart sound. Both these valves close at the same time so the hum is synchronized.
When the ventricles end their contraction and are going to relax for another contraction, the blood which they pumped through the aortic and pulmonary openings tends to flow back into the ventricles. This should not happen and thus these two openings are also guarded by valves, aortic and pulmonary valves respectively. The pressure in the aortic and pulmonary arteries is great and causes these two valves to shut close, producing another sound “dub”, known as second heart sound.
You might have noticed that as the first heart sound is produced when ventricles start to contract, we can also call it systolic sound (as systole refers to heart contraction). In contrast, as the second heart sound is produced when ventricles were relaxing, it is called diastolic sound (diastole means heart relaxation).
How to tell which one is first and which one is second while listening? The answer to this is quite simple, if you think about it. Put your fingers on any of the pulses, say carotid (you can also use radial pulse for that), and start listening to the heart. The sound which corresponds with the pulse will be the first heart sound, as it is coming when the ventricles are contracting, hence systolic sound.
Doctors know what normal sounds mean, they not only listen to the actual sounds but they are familiar with any increase or decrease in their pitch, quality, etc. Any other sounds, in addition to these two, are usually abnormal and are called murmurs. Even with your understanding, it can be judged that any added sound coming after the first heart sound will be a systolic murmur, which means something is wrong with either mitral or tricuspid valve and so on.
You must be having other questions out of curiosity, don’t hesitate to ask me in comments. Be vivid & stylish!