What are innocent heart murmurs?

What are innocent heart murmurs?

The normal heart beat produces two heart sounds, named first and second heart sounds. First heart sound is produced when the lower chambers of the heart contract. At this time, the valves between the upper and lower chambers close, producing the first heart sound. Second heart sound is produced when the lower chambers start relaxing after a contraction. They are produced by closure of the valves between the lower chambers and the great vessels arising from them. Occasionally, a third heart sound may be heard in normal children. A fourth heart sound may be heard in elderly sometimes. Otherwise the presence of third and fourth heart sounds are taken as abnormal. In addition to heart sounds, additional longer vibrations may be heard, which are called as heart murmurs. A heart murmur without heart disease is known as an innocent heart murmur. They are most often heard in children, due to the higher velocity of blood flow.

Other names which may be given for innocent murmurs are physiological murmur, normal murmur and even functional murmur. But the term innocent murmur is preferred as it strongly conveys that nothing is abnormal. Innocent heart murmurs are quite common in children. They are often detected when the blood flow velocity increases with fever. Less than 1% of murmurs in children are due to birth defects of the heart.

A common innocent murmur heard in children is called Still’s murmur. It was described by George Frederic Still in 1909. Still’s murmur is heard in the front of the chest, to the left of breast bone (sternum). Often it is a musical murmur, best heard when the child is lying down, decreasing in intensity when the child sits or stands.

Another common innocent murmur is a venous hum in the neck, due to the blood flow in the great veins returning blood to the heart. It disappears on light pressure over the great veins of the neck. It also changes with position and is better in the sitting position than in the lying down position, due to the effect of gravity. Looking down or the side may also make the venous hum inaudible.