Normal Heart Sounds

This section of the website helps you to learn about normal heart sounds including split and unsplit second heart sounds heard at various heart rates and auscultation points.  The standard auscultating points of heart sounds are mitral, tricuspid, aortic, and pulmonary areas. The normal heart sounds (S1 heart sound and S2 heart sound) are best heard at the tricuspid (left lower sternal border) and mitral ( cardiac apex).

Please use good quality headphones or earphones. Computer or phones speakers often fail to reproduce some heart sounds

Heart sounds may be defined as the sound produced in the heart during the cardiac cycle due to vibrations and are transmitted to the chest wall after transversing various structures of the chest cavity. First and second heart sounds are normally heard through the stethoscope. All the sounds can be recorded by a phonocardiogram. The first and second heart sounds are close to each other. After the second sound, there is a long pause. The sequence is like this first heart sound then second sound then pause; first heart sound then second sound then pause. Thus the sound goes on.

The sound is produced when the normal heart valve is closed. These ‘lub-dub’ sounds are caused by the closure of the atrioventricular (mitral and tricuspid) valves followed by the outlet (aortic and pulmonary) valves. The bell of the stethoscope transmits all sounds well but in some patients with high-frequency murmurs any additional low-frequency sound masks the high-frequency murmur. The bell is particularly useful at the apex and left sternal edge to listen for the diastolic murmur of mitral stenosis and third and fourth heart sounds.

The following diaphragm attenuates all frequencies equally, therefore making some low-frequency sounds less audible. Use the diaphragm to identify high-pitched sounds, e.g. early diastolic murmur of aortic regurgitation. Listen to it over the whole precordium for a pericardial friction rub.

Physiological basis/causes of heart sound

  1. The vibration of leaves of the valves during the closure
  2. The occurrence of turbulence during the rapid rush of blood from the atrium to the ventricle.

During medical practices, correct diagnosis and understanding of the case are important. So, while doing auscultation hearing the sounds correctly and identifying the abnormalities in it is important. Having prior practice to the sound will be a plus point for you, as we can do better in things we are familiar with. So, consider this site as a friend for you in gaining practice in auscultation and learning different cases regarding it. So, practice as much you want and gain your self-confidence and help for your future practices. This site will always be a friend that will help you learn about heart sounds.

First and Second Heart Sounds (Normal and Unsplit)

This sound is normal first and second heart sounds at 60 beats per minute


It occurs due to the sudden closure of A-V valves (tricuspid and mitral valves) at the onset of the ventricular systole.


  1. Nature: Dull, low pitched, prolonged duration: 0.15 sec.
  2. Sound like the word: L-U-B.
  3. Frequency: 25-45 HZ
  4. Area: it is best heard over the left 5th inter-coastal space just medial to mid-clavicular line.
  5. It coincides with the apex beat and carotid pulse and the spike of R-wave of ECG.


  • It indicates the clinical onset of ventricular systole.
  • The duration and intensity indicate the condition of the myocardium.
  • A clear first heart sound indicates that A-V valves are closing properly. Ie.e there is no incompetence.
  • Abnormalities of the intensity of the first heart sound

Abnormalities of the intensity of the first heart sound


  • Low cardiac output                          Long P-R interval (first-degree heart block)
  • Poor left ventricular function
  • Rheumatic mitral regurgitation


  • Increases cardiac output                 Short P-R interval atrial myxoma (rare)
  • Large stroke volume
  • Mitral stenosis


  • Atrial fibrillation                                complete heart block
  • Extrasystoles

First Heart Sound (Minimally Split)

The first heart sound is a combination of two separate sounds that are separated by very small intervals.

Among the two sounds, the mitral component comes first. The mitral component arises from the closure of the mitral valve. Then is the tricuspid component. This component arises from the closure of the tricuspid valve.

The mitral component is louder than the tricuspid component. The time interval between these two components that make up the first heart sound is 20-30 milliseconds.

Of the first heart sound, the normal variation is the minimally split.

Second Heart Sound (Physiologically Split)

An increase in the magnitude of the sound between the first and second components of heart sound is known as a physiological split of the second heart sound. This occurs due to the delay in the closure of the pulmonary valve. The inspiration causes prolongation of right ventricular mechanical systole. However, it seems reasonable from physiologic studies that inspiratory shortening of left ventricular systole resulting in an earlier aortic closure. This is not a pathological condition. The early closure of the aortic systole leads to the physiological split of the second heart.

Third Heart Sound (Physiologic)

The third heart sound ( S3 heart sounds) is a rare extra heart sound that occurs at the beginning of the middle of a third of diastole. This sound occurs soon after the normal heart sounds- first and second heart sounds.


Due to the sudden rapid rush of atrial blood into the ventricle during 1st RFP of ventricular diastole.


  1. Frequency: Low
  2. Duration: 0.04s (0.1s)
  3. It is heard in many normal young individuals.
  4. It can be recorded by a phonocardiogram.


Beginning of ventricular filling.

What is a Heart murmur?

A heart murmur is a sound that is produced by the rapid and turbulent flow of blood through the heart. The sounds could be whooshing or swishing. A heart murmur can be detected through the stethoscope.

Innocent Murmur

Innocent murmurs are murmurs produced by the normal flow. These murmurs are low-pitched sounds heard at the lower left sterna area. They are musical or have a relatively pure tone in quality or maybe squeaky. These most commonly occur between age 3 and adolescence. Among all the innocent murmurs, the still’s murmur is the most common innocent heart murmur. Still’s Murmur is not related to hearing or other problems. It is seen in children of age 3 to 6. Although it doesn’t need treatment, it can be diagnosed with a physical exam.

About 10% of adults and 30% of children (most between the ages of 3 and 7) have a harmless murmur called an innocent murmur. The conditions that may cause the innocent murmur are physical activity or strenuous exercises, pregnancy, fever, and anemia (The pale colorization of the skin and mucous membrane caused by decreased hemoglobin or RBC concentration in the blood).

Exercise – Heart Rate 120

Heart rate is defined as the number of heartbeats per minute your heart does. In young adults, it is about 60-90 beats/per min. the average is 72 beats min. Exercise or physical activity increases the heart rate (70-75% of the theoretical heart rate).

Exercises increase the intensity and the heart rate of the first heart sound. Some other conditions in which heart rates increases are hypertension, heart valve disease, heart failure, heart muscle diseases, tumors, infections, fever, and hyperthyroidism.

This increased heart rate sounds is best heard by the diaphragm of the stethoscope.

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