Why there is presence of pulmonary flow murmur?

Benign: In the majority of cases, a pulmonary flow murmur is a benign murmur that is audible due to healthy vigorous blood flow across the pulmonary outflow tract and/or a thin individual in which normal sounds are more easily detected. Many or most healthy children have pulmonary flow murmurs at one time or another.

Murmur: There is often a pulmonary flow murmur heard because the pulmonary artery is just under the chest wall adjacent to the sternum and noise in it is easily heard.