What is a heart "murmur"?

A heart murmur is NOT a disease . . . in fact, it may be present in a person with a normal heart. A murmur is simply a sound created by blood flow. Flow that is not obstructed, like in a wide-open hose, is hard to hear. However, when a hose is kinked, flow is no longer straight and uninterrupted. This disordered flow creates sound. In the human body, a similar situation can occur, and when the disordered flow is heard with a stethoscope, it is termed a murmur.
Murmurs can be caused by having a narrowed structure in the stream of blood, such as a stenotic valve. Likewise, the backward flow through a regurgitant valve occurs through a relatively small hole and causes sounds as well. The speed of flow is also increased in conditions such as exercise or fever, and this may cause straight or linear flow to become disrupted, even in normal structures. Thus, murmurs are common in this circumstance. Infants and children often have such sounds heard by medical professionals. When it is not caused by any abnormality of the heart, it is termed an "innocent murmur". The parent is generally told "not to worry about it" and that the "child will grow out of it". Both statements are correct when there is no underlying heart disease.