Heart murmur: An unusual, 'whooshing' heart sound that may be innocent or may reflect disease or malformation. A heart murmur is created by blood flow through a heart valve, by blood flow through a narrowed chamber, or by an unusual connection between the chambers, as seen with congenital heart disease. Sometimes a heart murmur does not represent any disease or condition and is, therefore, referred to as a functional heart murmur. There are many forms of heart murmurs representing a variety of heart conditions. Each type of murmur is characterized by its location, timing, duration, as well as the intensity and quality of the sound it makes. A heart murmur is usually heard by a physician while he or she listens to the chest with a stethoscope. While the heart murmur itself is never treated, sometime the condition it represents may require treatment.