What Causes The Heart Sounds?

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:42 PM IST

What Are Heart Sounds?

According to this use of the terminology, heart sounds are the sounds emitted by the closure of the heart valves and the flow of the blood in the heart chambers. First, the normal sounds S1 and S2 are the opening of the atrioventricular valves: tricuspid and mitral, and semilunar valves – pulmonary and aortic, respectively. They are useful for evaluating conditions concerning the heart’s performance and beat. Extra-systolic sounds, such as S3 and S4 or murmurs, suggest disease states like congestive heart failure, valvular diseases, and/or congenital anomalies. There is therefore need to distinguish and understand these sounds if any intervention or management of Cardiovascular diseases is to be done.

What Causes The Heart Sounds?

Primary Heart Sounds (S1 and S2)

The primary heart sounds are listed below:

First Heart Sound (S1)

Cause:

S1 also known as the first heart sound is the sound produced by the closure of the fourth atrioventricular valve; the mitral and tricuspid.

Timing:

This is at S1 that ventricular systole initiates and it is a phase whereby the ventricles contract to eject blood.

Characteristics:

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This sound is well known as the ‘lub’ sound and is louder and lasts longer than the second sound.

Second Heart Sound (S2)

Cause:

The second heart sound (S2) that is produced by the closure of semilunar valves includes aortic and pulmonary valves.

Timing:

S2 is widely viewed as concluding ventricular systole while the process of diastole is thought of as the process through which the ventricles remain open and eject their blood.

Characteristics:

This sound is known as ‘dub’; it is slightly different from S1 in the way that it is shorter than S1 and also has a sharper sound.

Additional Heart Sounds (S3 and S4)

The additional heart sounds are listed below:

Third Heart Sound (S3)

Cause:

S3 is produced by early diastolic filling of the ventricles as a result of blood being remarked into the relatively non-contracted ventricles by the atria.

Timing:

S3 is conducted after S2, this is perhaps in the first phase of the diastolic phase of the cardiac cycle.

Characteristics:

It is a loud, low-pitched sound sometimes referred to as a ventricular gallop and is worse with the diaphragm of the stethoscope.

Clinical significance:

S3 can be physiological in young individuals and physically fit individuals because of increased cardiac output, but in the elderly, it may be a sign of heart failure/volume overload.

Fourth Heart Sound (S4)

Cause:

S4 is produced by atrial systole against the closed and stiff or thick ventricles, resulting in increased blood turbulence.

Timing:

S4 happens immediately before S1, specifically in the beginning of diastroke as the atria eject blood onto the ventricles.

Characteristics:

It is a low-pitched, low-frequency murmur that is described as having an ‘atrial gallop;’ he heard best using the bell of the stethoscope.

Clinical significance:

S4 is normally seen in conditions that diminish the ventricles’ compliance, for example, hypertensive heart disease or left ventricular hypertrophy.

Abnormal Heart Sounds: Murmurs

The abnormal heart sounds are listed below:

Heart Murmurs

Causes:

Heart murmurs are noises associated with blood flow through and/or around the heart and its valves or from structural abnormalities in the heart, including stenosis and incompetence. These irregularities cause a turbulent circulation of blood and this as we all know is measured as a murmur.

Types:

Systolic Murmurs: They happen between S1 and S2 when ventricles are contracting. There are usual types such as those due to aortic stenosis or mitral regurgitation.

Diastolic Murmurs: Occur during ventricular diastole between S2 and S1 extremely close to each other. Examples of benign heart sounds include those produced by aortic stenosis or murmurs from it or murmurs from mitral stenosis.

Continuous Murmurs: Last the duration of the cardiac cycle such as those due to ductus arteriosus.

Clinical significance:

Heart murmurs are very vital in diagnosing heart diseases as well as judging the severity of the diseases. These may signify structural abnormalities of the heart and assist in the subsequent investigations and management plans.

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Frequently Asked Questions (FAQs)

1. What causes the first heart sound (S1)?

S1 is due to the closure of the atrioventricular valves, that is mitral and tricuspid valves during the phase of the initial systole. This closure makes an initial sound of ‘lub’, which is the sound of the heart contracting.

2. What is the difference between S1 and S2 heart sounds?

S1 is initiated at the onset of systole due to the closure of both the mitral and tricuspid valves whereas; S2 happens at the end of systole due to the closure of both the aortic and pulmonary valves. S1 is normally as loud format as a “lub” sound while S2 is in the format of a “dub” sound.

3. How are heart murmurs diagnosed?

Heart murmurs are identified via auscultation, making use of the stethoscope; any sounds that are abnormal during the cardiac cycle. In some cases, echocardiography, Doppler studies, and phonocardiography might be carried out to establish the cause, time, and kind of the murmur.

4. What does an abnormal heart sound indicate?

Thus, abnormal heart sounds like the extra sounds or murmurs can be indicative of different configurations or heart diseases like valve diseases, heart failures, or congenital heart diseases. It necessarily leads to web research to find out what has caused it to occur in the first place.

5. How can heart sounds be used to diagnose heart conditions?

Incorporating heart sounds into analysis of a patient’s condition offers useful information regarding their heart ailment. They include aorticans, pulmonicans, tricuspidans, and mitralans and their presence, timing and quality may be useful in diagnosing valve disorders, heart failure, and structural heart abnormalities. Although the modern medical context reserves the auscultation of heart sounds as a preliminary tool, its interpretation enables the diagnosis and planning of the eventual treatment.

6. What is the third heart sound (S3) and what does it indicate?

The third heart sound (S3) is an extra heart sound that occurs shortly after S2 during early diastole. It's caused by rapid ventricular filling. While it's normal in children and young adults, in older adults it can indicate conditions like heart failure or volume overload. S3 is often described as a "Kentucky gallop" because it sounds like a horse's canter.

7. How does the fourth heart sound (S4) differ from other heart sounds?

The fourth heart sound (S4) occurs just before S1 during late diastole. It's caused by the forceful contraction of the atria against a stiff or non-compliant ventricle. Unlike S1 and S2, which are valve closure sounds, S4 is a blood flow sound. It's always abnormal and can indicate conditions like hypertension, coronary artery disease, or hypertrophic cardiomyopathy.

8. Can heart sounds be affected by heart rate?

Yes, heart sounds can be affected by heart rate. As the heart rate increases, the duration between S1 and S2 (systole) shortens more than the duration between S2 and the next S1 (diastole). This can lead to a gallop rhythm in very rapid heart rates. Conversely, in slow heart rates, the distinction between the two sounds becomes more pronounced.

9. What is phonocardiography and how does it relate to heart sounds?

Phonocardiography is a method of recording heart sounds and murmurs as waveforms. It provides a visual representation of the acoustic events in the heart, allowing for more detailed analysis than auscultation alone. This technique can help in the precise timing of heart sounds, identification of subtle murmurs, and tracking changes in heart sounds over time.

10. What role does the stethoscope play in listening to heart sounds?

The stethoscope is crucial for auscultation (listening) of heart sounds. It amplifies the sounds and allows healthcare providers to hear them clearly. Different parts of the stethoscope (bell and diaphragm) are used to better hear different frequency sounds. The bell is better for low-frequency sounds like S1, while the diaphragm is better for higher-frequency sounds like S2 and some murmurs.

11. What are the main heart sounds and what causes them?

The two main heart sounds are "lub" (S1) and "dub" (S2). S1 is caused by the closure of the mitral and tricuspid valves at the beginning of ventricular systole. S2 is caused by the closure of the aortic and pulmonary valves at the beginning of ventricular diastole. These sounds are produced by the vibration of the heart valves and surrounding structures as blood flow suddenly stops.

12. Why do we hear two distinct heart sounds instead of one continuous sound?

We hear two distinct heart sounds because they occur at different phases of the cardiac cycle. The first sound (S1) happens at the start of ventricular contraction, while the second sound (S2) occurs at the beginning of ventricular relaxation. The pause between these sounds represents the periods of systole and diastole when blood is flowing through the heart chambers.

13. How does blood flow relate to heart sounds?

Heart sounds are directly related to blood flow. The sounds are produced when blood flow is abruptly stopped by the closing of heart valves. The first heart sound (S1) occurs when blood flow from the atria to the ventricles is stopped by the closure of the atrioventricular valves. The second heart sound (S2) is produced when blood flow from the ventricles to the great arteries is halted by the closure of the semilunar valves.

14. How do the heart valves contribute to heart sounds?

Heart valves play a crucial role in producing heart sounds. The sudden closure of these valves creates vibrations in the blood and surrounding heart tissues, which we perceive as sounds. The first heart sound (S1) is produced by the closure of the mitral and tricuspid valves, while the second heart sound (S2) is caused by the closure of the aortic and pulmonary valves.

15. What is the significance of the timing of heart sounds in the cardiac cycle?

The timing of heart sounds is significant as it marks key events in the cardiac cycle. S1 marks the beginning of ventricular systole (contraction), while S2 marks the beginning of ventricular diastole (relaxation). This timing helps healthcare professionals assess the heart's function and identify any abnormalities in the cardiac cycle.

16. What is the difference between intrinsic and extrinsic heart sounds?

Intrinsic heart sounds are those produced within the heart itself, primarily by valve closures (S1 and S2) and blood flow dynamics (S3 and S4). Extrinsic heart sounds, also called adventitious sounds, are produced outside the heart but are heard during cardiac auscultation. These include pericardial friction rubs, pleural rubs, and lung sounds that may be mistaken for cardiac sounds.

17. What is the physiological basis for the loudness of heart sounds?

The loudness of heart sounds is primarily determined by the abruptness of valve closure and the pressure gradient across the valve at the time of closure. Factors that increase these, such as increased blood pressure or ventricular contraction force, can make heart sounds louder. Additionally, the volume of blood in the heart, the proximity of the heart to the chest wall, and the condition of the surrounding tissues all influence the perceived loudness of heart sounds.

18. How do heart sounds differ between children and adults?

Heart sounds in children are generally louder and clearer than in adults due to thinner chest walls and smaller body size. Children also commonly have a physiological split of the second heart sound during inspiration, which is considered normal. As people age, heart sounds may become softer due to factors like increased chest wall thickness and reduced cardiac function.

19. What is the relationship between heart sounds and pulse?

Heart sounds and pulse are closely related but not identical. The first heart sound (S1) occurs slightly before the carotid pulse is felt, as it marks the start of ventricular contraction. The pulse felt in peripheral arteries is delayed compared to heart sounds due to the time it takes for the pressure wave to travel through the arteries. Understanding this relationship is important for accurate clinical assessment.

20. What is the role of electronic stethoscopes in analyzing heart sounds?

Electronic stethoscopes enhance the ability to analyze heart sounds by amplifying and filtering the sounds. They can reduce background noise and some models can even record and visualize the sounds. This allows for more detailed analysis, comparison over time, and sharing with other healthcare providers. Some advanced electronic stethoscopes incorporate artificial intelligence to assist in identifying and classifying heart sounds and murmurs.

21. What is a heart murmur and how does it relate to normal heart sounds?

A heart murmur is an abnormal sound heard between the normal heart sounds. It's typically caused by turbulent blood flow through the heart valves or within the heart chambers. While normal heart sounds are brief "lub-dub" sounds, murmurs are often described as whooshing or swishing sounds. Murmurs can indicate various heart conditions, including valve problems or congenital heart defects.

22. How can changes in body position affect heart sounds?

Changes in body position can affect heart sounds by altering blood flow and the heart's position relative to the chest wall. For example, leaning forward can accentuate certain murmurs, while lying on the left side can make the mitral valve sounds more audible. These positional changes are often used during cardiac examinations to better evaluate heart sounds and murmurs.

23. How do heart sounds differ in various types of valvular heart disease?

In valvular heart disease, heart sounds can be significantly altered. For instance, in mitral stenosis, S1 may be louder and S2 may be softer. In aortic stenosis, S2 might be soft or absent. Regurgitant lesions often produce murmurs that can mask or alter the normal heart sounds. The specific changes in heart sounds can provide valuable clues about the type and severity of valvular disease.

24. How do congenital heart defects affect heart sounds?

Congenital heart defects can significantly alter heart sounds. For example, a ventricular septal defect often produces a loud, harsh systolic murmur. Atrial septal defects may cause a fixed split S2. Patent ductus arteriosus typically results in a continuous "machinery" murmur. The specific changes in heart sounds depend on the type and severity of the defect, and can be crucial in diagnosis and monitoring of these conditions.

25. What is the difference between functional and pathological heart murmurs?

Functional (or physiological) murmurs are benign sounds produced by blood flow in a structurally normal heart. They're common in children and young adults, often vary with respiration or position, and don't indicate heart disease. Pathological murmurs, on the other hand, are caused by structural abnormalities in the heart, such as valve defects or septal defects. They tend to be louder, longer, and associated with other signs of heart disease. Distinguishing between these types is crucial for proper diagnosis and management.

26. What is the role of digital signal processing in analyzing heart sounds?

Digital signal processing plays a crucial role in modern analysis of heart sounds. It allows for filtering out background noise, amplifying specific frequency ranges, and visualizing sound patterns. Advanced algorithms can automatically detect and classify heart sounds and murmurs, potentially improving diagnostic accuracy. This technology is particularly useful in telemedicine applications, allowing for remote analysis of heart sounds and aiding in early detection of cardiac abnormalities.

27. How do artificial heart devices affect heart sounds?

Artificial heart devices, such as ventricular assist devices (VADs) or total artificial hearts, significantly alter heart sounds. These devices often produce continuous humming or whirring

28. How does the intensity of heart sounds vary and what does this indicate?

The intensity of heart sounds can vary based on factors such as the force of valve closure, the amount of blood in the heart, and the proximity of the heart to the chest wall. Louder sounds may indicate conditions like hypertension or anemia, while softer sounds might suggest heart failure or obesity. Variations in intensity between S1 and S2 can also provide clues about specific heart conditions.

29. What is the split second heart sound and what causes it?

The split second heart sound occurs when there's a slight delay between the closure of the aortic and pulmonary valves. This is normal during inspiration when increased blood return to the right side of the heart causes the pulmonary valve to close slightly after the aortic valve. An abnormally wide split or a split that doesn't vary with respiration can indicate certain heart conditions.

30. How do heart valve prosthetics affect heart sounds?

Heart valve prosthetics can significantly alter heart sounds. Mechanical valves typically produce a distinct clicking sound upon closure, which is louder and higher-pitched than natural valve sounds. Bioprosthetic valves, made from animal tissue, produce sounds more similar to natural valves but may still be distinguishable. The presence of prosthetic valve sounds can help confirm proper valve function.

31. How do respiratory cycles influence heart sounds?

Respiratory cycles can significantly influence heart sounds. During inspiration, increased venous return to the right side of the heart can cause a physiological split of S2, as the pulmonary valve closes slightly after the aortic valve. Expiration typically causes the split to narrow or disappear. Some heart murmurs may also vary with respiration, becoming louder during inspiration (right-sided murmurs) or expiration (left-sided murmurs).

32. How do heart sounds change during pregnancy?

During pregnancy, several changes in heart sounds can occur. The increased blood volume and cardiac output can lead to louder heart sounds and a physiological S3. A soft systolic murmur is common due to increased blood flow. The split of S2 may become more pronounced due to the enlarged uterus pushing up on the diaphragm, affecting venous return. These changes are usually benign but require careful evaluation to distinguish from pathological conditions.

33. What is the significance of a gallop rhythm in heart sounds?

A gallop rhythm occurs when either S3 or S4 (or both) are audible in addition to the normal S1 and S2. It's called a gallop because it resembles the sound of a horse's gallop. An S3 gallop in adults often indicates heart failure or volume overload. An S4 gallop suggests decreased ventricular compliance, often seen in conditions like hypertension or coronary artery disease. The presence of a gallop rhythm usually indicates significant cardiac pathology and requires further evaluation.

34. How do heart sounds change with age?

Heart sounds typically change with age due to various physiological and anatomical changes. In children, heart sounds are usually louder and clearer due to thinner chest walls. A physiological S3 is common in young adults but becomes abnormal in older adults. As people age, heart sounds may become softer due to increased chest wall thickness and reduced cardiac function. The likelihood of hearing an S4 increases with age due to decreased ventricular compliance.

35. What is the relationship between heart sounds and electrocardiogram (ECG) findings?

Heart sounds and ECG findings are closely related as they both reflect the cardiac cycle. S1 occurs shortly after the QRS complex on the ECG, which represents ventricular depolarization. S2 occurs around the end of the T wave, which represents ventricular repolarization. Abnormalities in heart sounds often correlate with ECG changes. For example, a split S2 might be reflected in a widened QRS complex. Combining auscultation with ECG analysis provides a more comprehensive assessment of cardiac function.

36. How do different types of cardiomyopathy affect heart sounds?

Different types of cardiomyopathy can distinctly affect heart sounds. In hypertrophic cardiomyopathy, a systolic murmur may be heard due to outflow obstruction, and S4 might be present due to decreased ventricular compliance. Dilated cardiomyopathy often presents with an S3 gallop due to rapid ventricular filling into a dilated chamber. Restrictive cardiomyopathy might produce both S3 and S4 gallops. The specific changes in heart sounds can provide valuable clues about the type and severity of cardiomyopathy.

37. What is the importance of the location of maximum intensity for heart sounds?

The location of maximum intensity for heart sounds is crucial for accurate diagnosis. Different heart valves and cardiac events are best heard at specific locations on the chest wall. For example, mitral valve sounds are typically loudest at the apex of the heart, while aortic valve sounds are best heard at the right upper sternal border. Understanding these locations helps in identifying the origin of normal and abnormal heart sounds, aiding in the diagnosis of various cardiac conditions.

38. How do pericardial diseases affect heart sounds?

Pericardial diseases can significantly alter heart sounds. In pericardial effusion, heart sounds may become muffled due to the fluid surrounding the heart. Constrictive pericarditis can produce a pericardial knock, an early diastolic sound similar to S3. Pericarditis often causes a friction rub, a scratchy sound heard throughout the cardiac cycle. These changes in heart sounds are important diagnostic clues for pericardial conditions.

39. How do heart sounds change during exercise?

During exercise, heart sounds typically become louder and faster due to increased heart rate and cardiac output. S1 may become more pronounced due to more forceful ventricular contraction. The interval between S1 and S2 shortens as systole becomes briefer. Some physiological murmurs may become more noticeable. In individuals with heart disease, exercise can exacerbate abnormal heart sounds or produce new ones, which is why exercise stress tests are valuable diagnostic tools.

40. How do heart sounds differ in right-sided versus left-sided heart failure?

In right-sided heart failure, signs of right ventricular overload may be present, such as a loud P2 component of S2 due to pulmonary hypertension. A right-sided S3 gallop might be heard best at the left lower sternal border. In left-sided heart failure, a left-sided S3 gallop is often heard at the apex, indicating volume overload. Mitral regurgitation murmur may also be present. The differences in heart sounds between right and left-sided failure reflect the distinct pathophysiology of each condition.

41. What is the significance of a fixed split S2 heart sound?

A fixed split S2 is when the split between the aortic and pulmonic components of the second heart sound doesn't vary with respiration. This is abnormal, as the split typically widens during inspiration and narrows during expiration. A fixed split S2 is often indicative of an atrial septal defect, where the left-to-right shunt maintains a constant volume load on the right ventricle throughout the respiratory cycle. It can also occur in conditions like right bundle branch block or severe pulmonary hypertension.