Heart sounds are the sounds produced by mechanical activities of heart during each cardiac cycle.

Heart Sounds Are Produced By

1. Flow of blood through chambers of heart.
2. Contraction of cardiac muscle.
3. Closure of valves of the heart.

Heart sounds are heard by placing the ear over the chest or by using a stethoscope. These sounds are also recorded graphically.

Different Heart Sounds

Four heart sounds are produced during each cardiac cycle.

Importance of Heart Sounds

Evaluation of heart sounds has important diagnostic value in clinical practice because alteration in heart sounds indicates the cardiac diseases involving valves of the heart.

First heart sound is produced during isometric contraction period and earlier part of ejection period.

Causes of First Heart Sound

Major cause for first heart sound is the sudden and synchronous (simultaneous) closure of atrioventricular valves.

In addition to this, ejection of blood from ventricles into aorta and pulmonary artery and contraction of cardiac muscles also contribute in the production of the first heart sound.

Characteristics of First Heart Sound

• Long, soft and low-pitched sound.
• Resembles the spoken word “LUBB” (or LUB).
• Duration: 0.10 to 0.17 second.
• Frequency: 25 to 45 cycles/second.

First Heart Sound and ECG

First heart sound coincides with peak of ‘R’ wave in ECG.

Applied Physiology: Reduplication of First Heart Sound

Reduplication means splitting.

First heart sound is split when the atrioventricular valves do not close simultaneously (asynchronous closure).

Physiological splitting (in normal conditions) is rare.

Pathological splitting of first heart sound occurs in stenosis of atrioventricular valves and atrial septal defect.

Second heart sound is produced at the end of protodiastolic period.

Cause for Second Heart Sound

Second heart sound is produced due to the sudden and synchronous closure of semilunar valves.

Characteristics of Second Heart Sound

• Short, sharp and high-pitched sound.
• Resembles the spoken word “DUBB” (or DUP).
• Duration: 0.10 to 0.14 second.
• Frequency: 50 cycles/second.

Second Heart Sound and ECG

Second heart sound coincides with the ‘T’ wave in ECG.

Sometimes, it may precede or it may commence after the peak of ‘T’ wave.

Applied Physiology: Reduplication of Second Heart Sound

Splitting of second heart sound occurs due to asynchronous closure of semilunar valves.

It may occur both in physiological and pathological conditions.

Third heart sound is a low-pitched sound that is produced during rapid filling period of the cardiac cycle.

Usually, the third heart sound is inaudible by stethoscope and it can be heard only by using microphone.

Cause for Third Heart Sound

Third heart sound is produced by the rushing of blood into ventricles during rapid filling phase.

Characteristics of Third Heart Sound

• Short and low-pitched sound.
• Duration: 0.07 to 0.10 second.
• Frequency: 1 to 6 cycles/second.

Third Heart Sound and ECG

It appears between ‘T’ and ‘P’ waves of ECG.

Applied Physiology: Conditions When Third Heart Sound Becomes Audible by Stethoscope

Third heart sound can be heard by stethoscope in children and athletes.

Pathological conditions when third heart sound becomes loud and audible by stethoscope are:

• Aortic regurgitation
• Cardiac failure
• Cardiomyopathy with dilated ventricles

Normally, the fourth heart sound is an inaudible sound.

It becomes audible only in pathological conditions.

It is studied only by graphical recording, i.e. phonocardiography.

Cause for Fourth Heart Sound

Fourth heart sound is produced by contraction of atrial musculature during atrial systole.

Characteristics of Fourth Heart Sound

• Short and low-pitched sound.
• Duration: 0.02 to 0.04 second.
• Frequency: 1 to 4 cycles/second.

Fourth Heart Sound and ECG

Fourth heart sound coincides with the interval between the end of ‘P’ wave and onset of ‘Q’ wave.

Applied Physiology: Conditions When Fourth Heart Sound Becomes Audible

Fourth heart sound becomes audible by stethoscope when the ventricles become stiff.

Ventricular stiffness occurs in conditions like:

• Ventricular hypertrophy
• Longstanding hypertension
• Aortic stenosis

In these conditions, to overcome the ventricular stiffness, atria contract forcefully producing audible fourth heart sound.

Triple Heart Sound or Gallop Rhythm

Triple heart sound or triple rhythm is an abnormal rhythm of heart, characterized by three clear heart sounds during each heartbeat.

It is due to an abnormal third or fourth heart sound that is heard besides first and second heart sounds.

It is also called gallop rhythm, since it resembles the sound of a horse’s gallop.

Usually, it is indicative of serious cardiovascular disease.

Triple heart sound is produced in conditions like myocardial infarction and severe hypertension.

Quadruple Heart Sound

Quadruple heart sound is an abnormal rhythm of heart, characterized by four clear heart sounds during each heartbeat.

It is also called quadruple rhythm.

It is due to third and fourth heart sounds that are heard besides first and second heart sounds.

It is also called quadruple gallop.

Quadruple heart sound is also indicative of serious cardiovascular disease.

Quadruple heart sound is produced in patients with congestive heart failure.

Summation Gallop

Whenever, there is tachycardia in patients with quadruple heart sound, the third and fourth heart sounds merge together and give rise to summation gallop sound.

This sound is called summation gallop and resembles gallop rhythm.

Heart sounds are studied by three methods:

I. By Using Stethoscope: Auscultation Areas

First and second heart sounds are heard on auscultation areas by using the stethoscope.

The chest is divided into four areas which are called auscultation areas.

1. Mitral Area (Bicuspid Area)

Mitral area is in the left 5th intercostal space halfway between medial to midclavicular line.

Sound produced by closure of mitral valve (first heart sound) is heard well into this area.

It is also called apex beat area because apex beat is felt in this area.

2. Tricuspid Area

Tricuspid area is on the left border of lower end of sternum.

Sound produced by closure of tricuspid valve (first heart sound) is transmitted well to this area.

3. Pulmonary Area

Pulmonary area is on the left 2nd intercostal space close to sternum.

Sound produced by closure of pulmonary valve (second heart sound) is heard well in this area.

4. Aortic Area

Aortic area is over the right 2nd intercostal space, close to sternum.

On this area, the sound produced by closure of aortic valve (second heart sound) is heard well.

II. By Using Microphone

A highly sensitive microphone is placed over the chest.

Heart sounds are amplified by means of an amplifier and heard by using a loudspeaker.

First, second and third heart sounds are heard by this method.

III. By Phonocardiogram

Phonocardiography is the technique used to record the heart sounds.

Phonocardiogram is the graphical record of heart sounds.

It is done by placing an electronic sound transducer over the chest.

This transducer is connected to a recording device like polygraph.

All four heart sounds can be recorded by phonocardiogram.

It helps to analyze the frequency of the sound waves.

First Heart Sound

First heart sound is recorded as single group of waves which are small amplitude to start with.

Later, the amplitude rapidly rises and falls to form crescendo and diminuendo series of waves.

About 9 to 13 waves appear.

Second Heart Sound

Second heart sound appears as single group of waves, which have same amplitude.

About 4 to 6 waves are recorded.

Third Heart Sound

Third heart sound is found in phonocardiogram with only 1 to 4 waves grouped together.

Fourth Heart Sound

Fourth heart sound mostly merges with first heart sound.

If it appears as separate form, it has 1 to 2 waves with very low amplitude.

Cardiac murmur is the abnormal or unusual heart sound.

Cardiac murmur is also called abnormal heart sound or cardiac bruit.

Abnormal sound is produced because of change in the pattern of blood flow.

Normally, blood flows in streamline through the heart and blood vessels.

However, during abnormal conditions like valvular diseases, the blood flow becomes turbulent.

It produces the cardiac murmur.

Methods of Hearing Cardiac Murmur

Cardiac murmur is heard by placing the chest piece of the stethoscope over the auscultatory areas.

Murmur due to disease of a particular valve is heard well over the auscultatory area of that valve.

Sometimes, the murmur is felt by palpation of the chest.

Some patients are heard with the murmur at a distance of few feet away from the patient.

Causes of Cardiac Murmur

Cardiac murmur is produced because of change in the pattern of blood flow.

Normally, blood flows in streamline through the heart and blood vessels.

However, during abnormal conditions like valvular diseases, the blood flow becomes turbulent.

Murmur is produced because of valvular diseases, septal defects and vascular defects.

Valvular diseases are of two types:

Cardiac murmur is classified into three types:

1. Systolic murmur
2. Diastolic murmur
3. Continuous murmur

Systolic murmur is produced during systole.

It is produced in the following conditions:

1. Incompetence of Atrioventricular Valves

Weak atrioventricular valves cannot close completely.

It causes regurgitation of blood from ventricles to the atria during ventricular systole, producing a harsh blowing sound with high frequency.

2. Stenosis of Semilunar Valves

During stenosis of aortic valve, left ventricular pressure rises up to 300 mm Hg during systole.

This produces a greater turbulence in the blood flow.

Vibrations of this sound can be felt as “thrills” by palpation over lower neck region and upper chest.

In severe conditions, the sound is heard even a few feet away from affected person.

It is a harsh and loud sound.

3. Murmur Due to Anemia

A systolic murmur is heard in severe anemia because of reduced viscosity and accelerated flow of blood.

4. Septal Defect

During interventricular septal defect, blood flows from left ventricle to right ventricle during systole.

It produces a systolic murmur.

Septal defect is a rare disorder.

5. Coarctation of Aorta

Coarctation of aorta is a congenital disorder, characterized by the narrowing of a part of systemic aorta.

A loud murmur is produced during systole and it is heard in the earlier part of diastole also.

Diastolic murmur is produced during diastole.

It is produced in the following conditions:

1. Stenosis of Atrioventricular Valves

When atrioventricular valves become narrow, turbulence of blood flow occurs during diastole, i.e. when blood enters the ventricles from atria.

Murmur due to stenosis of mitral valve is heard better at mitral area.

Murmur due to stenosis of tricuspid valve is heard best at tricuspid area.

It is a weak sound with low frequency.

Sometimes, murmur due to mitral stenosis cannot be heard by stethoscope, due to low frequency.

But it can be felt as a mild thrill over mitral area of the chest.

2. Incompetence of Semilunar Valves

Murmur is produced during regurgitation of blood from aorta into the ventricle, through incompetent semilunar valve during diastole.

It is like a blowing sound with low frequency.

Continuous murmur is heard in conditions such as patent ductus arteriosus.

Patent Ductus Arteriosus

Intact ductus arteriosus is called patent ductus arteriosus.

A continuous murmur is heard in this condition.

However, intensity of the sound is more during systole and less during diastole.

Because of this, it is also called machinery murmur.