Cardiac Murmur and its causes

Cardiac murmur is the abnormal or unusual heart sound. It is also called abnormal heart sound or cardiac bruit. Cardiac murmur is heard by stethoscope, along with normal heart sounds. Cardiac murmur is heard by placing chest piece of 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 as ‘thrills’. In some patients, murmur is heard without any aid, even at a distance of few feet away from the patient.

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. It produces the cardiac murmur.

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

Valvular Diseases

Valvular diseases are of two types:

1. Stenosis

2. Incompetence.

1. Stenosis

Stenosis means narrowing of heart valve. Blood flows rapidly with turbulence through the narrow orifice of the valve, resulting in murmur.


Incompetence refers to weakening of the heart valve. When the valve becomes weak, it cannot close properly. It causes back flow of blood, resulting in turbulence. This disease is also called regurgitation or valvular



Cardiac murmur is classified into three types:

A. Systolic murmur

B. Diastolic murmur

C. Continuous murmur.


Systolic murmur is the murmur which is produced during systole. It is produced in the following conditions:

1. Incompetence of Atrioventricular Valves

When the atrioventricular valves become weak, these valves cannot close completely. It causes regurgitation of blood from ventricles to the atria during ventricular systole, producing the murmur. It is a harsh blowing sound with high frequency.

2. Stenosis of Semilunar Valves

During stenosis of aortic valve, the left ventricular pressure raises up to 300 mm Hg during systole. It causes a greater turbulence in the blood flow. The vibrations of this sound can be felt as ‘thrills’ by palpation over lowerneck region and upper chest. In severe conditions, the sound is heard even a few feet away from the affected person. It is a harsh and a 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 the murmur that is produced during diastole. It is produced in the following conditions:

1. Stenosis of Atrioventricular Valves

When the atrioventricular valves become narrow, the 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 the 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 the murmur that 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. It is a harsh blowing sound and is heard best in the pulmonary area. The murmur is heard 1 year after birth

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