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What are Heart Sounds?

Rutuja Jathar
Heart sound is made by the heart through its rhythmic beating. Normally it is heard as a 'Lub Dub' sound. However, in some medical conditions, there could be some more sounds involved. Basic knowledge about heart sounds is needed to recognize the symptoms of serious ailments.
Heart sounds are a normal and involuntary process. In cardiac auscultation, they can be easily heard by placing a stethoscope on your chest. The 'Lub' is the first sound or the (S1), while Dub is second one or the (S2).
Basically these vibrations are produced by the rhythmic contraction and relaxation of the bicuspid/mitral valves, the tricuspid valves, the aortic and the pulmonic valves.
When there are any changes in these sounds, they are termed as heart murmurs and adventitious sounds; S3 and S4 respectively. These are also called gallop rhythms. They can be divided into two types - normal (heartbeat) and abnormal heart sounds.

Normal Heart Sounds

Both S1 and S2 are the results of the reverberation of blood within the valves of the heart. Let's have a look at these types individually:
S1: This sound is heard at the time of the systole, which is better known as the ventricular contraction. The cause of this sound is basically the closure of the bicuspid/mitral and tricuspid valves. The closing of these valves prevent reverse blood flow from ventricle to the arteries.
Ventricular contraction and the contraction of the papillary muscles occurs at the same time. This closes the cusps of the valves to avoid the valves blowing into the atria. This procedure is very essential because the ventricular pressure is very high at that time.
S2: The second sound occurs at the end of the systole; which is the start of a diastole. It is audible when the pulmonary and the aortic semilunar valves are closed.
When the left ventricle is empty; ventricular pressure is lesser than the pressure in the aorta. This causes the aortic blood to flow back into the left ventricle. This flow is stopped by the contraction of the aortic valve. Likewise, when the pressure in the right ventricle gets below the pressure in the pulmonary artery, the pulmonary valve gets closed.

Abnormal Heart Sounds

It takes a lot of skill to investigate these 'abnormal' sounds. There are various methods to observe them. The main tools are - Electrocardiogram(ECG), chest x-rays, cardiac auscultations, and electrocardiography. The severity of the vibrations depends on their frequency and the density. Let's discuss these individually:
Split S2: Split S2 can be found on the cardiac auscultation of the S2. It happens due to normal physiological respiration. Normally, it is heard during inspiration and when the aortic valves and the pulmonary valves, fail to close in a synchronized manner. These splits are:
Physiological Split: The negative intrathoracic pressure increases during the inspiration and results in the expansion of the lung. It also increases the volume of the blood returning from the body to the right ventricle and reduces the blood volume returned from the lungs to the left ventricle.
As a result, the pulmonary valves stay open during the systole and the aortic valves close earlier than normal. Hence the pulmonic component of the S2 delays relative to the aortic A2 component. This delay is heard as a slight "splitting" of the S2. The difference between the two sounds is less than 30msec.
This can normally be heard in young people at the time of inspiration in the pulmonary area. It is more clear in the 2nd left intercostal space. During expiration, the intrathoracic pressure is less compared to inspiration. It fails to perform its normal function. As a result the pulmonary valve closes earlier and overlaps the A2.
Pathological Split: Pathological significance depends on the degree of split. When the degree of the split is maximum, the chances of the heart getting damaged are higher. These splittings of the second sound could be caused by different reasons:

1) Normal or Physiological splitting - normal
2) Wide, fixed, splitting - Atrial septal defect
3) Wide split, (varies with every inspiration) - Pulmonary stenosis, RBBB (Right Bundle branch block )
4) Paradoxical splitting - Hypertrophic cardiomyopathy
5) Loud Aortic Component - Systemic hypertension or Dilated aortic root
6) Soft Aortic Component - Calcific aortic stenosis
7) Loud Pulmonary Component - Pulmonary hypertension
S3It occurs quickly after the first two heart sounds. During the early diastole it can be heard 0.12 to 0.18 seconds after the S2. It is audible through a stethoscope. And it's normal in the people below 40 years of age. As the atrial pressure increases, so does the blood flow rate.
The main causes of Sis 'congestive heart failure' along with 'Post Myocardial Infarction' and 'Associated Dilated Cardiomyopathy with dilated ventricles'. In some rare cases regurgitation of the mitral valve may also result into the third sound. Increase of blood flow due to left to right shunts is also one of the reasons.
S4: This is also a low frequency sound which can be heard during the presystolic period of diastole. It is sometimes audible in athletes and children. It's caused by a major disturbance in the blood flow, but when loud it signifies a total failure of the left ventricle.
If so, it can be heard in the cardiac apex. If the problem is with the right ventricle then it is audible in the sternum and its lower left hand side. The main causes are hypertension, aortic stenosis, throttled left ventricle, ischemic cardiomyopathy, or hypertrophic cardiomyopathy. Both S3 and S4 are also known as ventricular gallop.


Heart murmurs are the product of the audible noises of turbulent blood flow, through the heart valves. They are the whooshing and rasping sounds. When the valves do not close tightly, murmurs occur, because the blood leaks backwards.
The degree, location, and timing of the murmur are the most important factors. An ECG is the best way to find the exact cause of the murmur. It's not always linked to any severe disorder. Murmurs are mainly classified into two types as Systolic and Diastolic murmurs.
Aortic regurgitation, Aortic Stenosis, idiopathic hypertrophic subaortic stenosis (hypertrophic cardiomyopathy), Pulmonary stenosis, chronic mitral regurgitation, mitral stenosis, tricuspid regurgitation, acute mitral regurgitation, tricuspid stenosis are the significant causes of the murmurs.
Sometimes the murmurs could also be heard in children. The main causes of these murmurs are Atrial Septal Defect (ASD), Patent Ductus Arteriosus (PDA), Coarctation of the Aorta and Ventricular Septal Defect (VSD). Murmurs such as Venous hum, Still's murmur and Pulmonary flow murmurs are a normal part of their development and don't need any special treatment.
Murmurs can be classified into seven types according to their location, intensity, degree, time, size, pitch, and radiation. Rheumatic fever, pregnancy, high blood pressure, anemia, or overactive thyroid glands could be the reasons for a heart murmur. 


This abnormal sound appears if there is a sudden pause in the functioning of the semilunar valve. It is commonly heard in the early systolic period. Following are the various types of clicks:
Aortic Ejection Click: These are loud sounds of high frequency heard at the time of murmurs and have the same etiology. They are heard with calcific aortic stenosis because of the non-mobile valves. They are mainly caused by aortic stenosis, pulmonic stenosis, pulmonary hypertension, and dilated pulmonary trunk, mitral aortic valves, and dilated aortic root.
Pulmonic Ejection Click: These sounds occur in the early systolic phase. They are associated with murmurs and often fade away with inspiration. They are formed in the 2nd and 3rd edge of the intercostal space.
Midsystolic Click: It is also referred as late systolic murmur syndrome or more commonly known as "mitral valve prolapse". There are not many visible symptoms of this disease. People can lead their lives normally even after getting diagnosed with mitral valve prolapse. It's mostly seen in the women aging 20-40, some men also get affected by it.

Opening Snap

These sounds are related to mitral stenosis. They occur during the early diastole, around 50-100 ms after the aortic valve A2 closes. These sounds are heard in the left lower sternal border and often fade away with inspiration. If the opening snaps are with a slow murmur, it indicates mitral stenosis. Timing of opening snap is vital in deciding the severity.


People suffering with pericarditis, or inflammation of the pericardium, may get to hear a pericardian rub. This is a type of scratching, and high-pitched sound produced by the rubbing of the layers of swollen pericardium. They can be heard in the diastole, but they are the loudest during the systole.
All these sounds can be produced by the heart. Some of them are serious and some not so serious. However, now that you know what are heart sounds, you better listen carefully to avoid any disastrous health conditions!
Disclaimer: This is for informative purposes only, and should not be used as a replacement for expert medical advice.