The human heart consist of four chambers which will alternate blood within these chambers throughout the cardiac cycle in order to receive blood from the rest of the body, oxygenate the received blood by sending it to the lungs, receive oxygenated blood from the lungs and re-distribute the oxygenated blood throughout the body to sustain tissue functions. The mechanisms that are in place within the heart act in such a way to prevent blood from reversing its direction at any time of the cycle and will always separate the oxygenated blood from the oxygen depleted blood.
What are the normal heart sounds?
When the cardiac cycle or the contraction and relaxation cycle of the heart is going on, it would be possible to hear two distinguishable sounds that occurs one after another in what is known as the ‘lub dub’ tone. In a normal heart, these sounds will occur at a regular pattern and is related to the filling and emptying or else the ‘systole’ and the ‘diastole’ of the cardiac cycle.
During systole, the ventricles of the heart will contract in order to force the blood within the ventricles into the aorta and pulmonary artery. While doing so, there is a possibility of blood from the ventricle entering the path which it took to arrive at this chamber that is towards the atria. As such, the two valves which are known as mitral and tricuspid will close with the contraction of its attached tendinae as well as the papillary muscles and prevent the backflow from taking place. This closure of the atrio-ventricular valves gives rise to the sound, ‘lub’ or in other words S1.
When the ventricles begin to relax, the pressure within the left and the right ventricles will fall below the aorta and the pulmonary artery respectively and therefore has the possibility of reversed flow, back towards the ventricles. The mechanism that prevents such back flow would be the presence of aortic and pulmonary valves at its origin and their closure will lead to the characteristic ‘dub’ sound or else the S2.
S3 and S4:
Apart from these two sounds, there may be two other heart sounds named as S3 and S4. These sounds can be heard in normal individuals such as trained athletes, children and in youth, whereas if they present in adults, would indicate the presence of certain types of heart diseases such as ventricular failure, congestive cardiac failure and restrictive cardiomyopathy. But, it should be remembered that, these heart sounds are relatively rare when considering normal heart sounds.