To explain cardiac murmur it is necessary to familiar with activities of heart.

Heart has two activities:

1- Electrical activity which leads to mechanical activity

2- Mechanical activity which produces heart sounds.

Electrical activity can be showed as a wave which is named electrocardiogram-ECG.

Actually contraction of heart muscles, opening and closing heart valves also flow of blood in heart chambers lead to heart sounds.

When the heart is in contractile position it is named systolic period and when it is in relax situation it is named diastolic period.These two periods  produce special sounds similar to LUP and DUP pronunciation respectively which can be listened by a stethoscope.They are named systolic and diastolic sound.

Normally there is no additional sound  between LUP and DUP. Any additional sound is cardiac murmur .Cardiac murmur is classified as systolic murmur, diastolic murmur and if additional sound is listened in systolic and diastolic period it is named machinery murmur.

Cardiac murmur can be physiologic or pathologic. Pathological forms need treatment.