What is the primary cause of the heart murmur detected in the infant during the well-child examination?

In infants, heart murmurs are often due to increased blood flow across the valves, particularly in the case of the pulmonic valve. This is especially common in newborns and younger children, where high flow states can lead to the presence of innocent or functional murmurs. These murmurs typically arise from turbulence in the blood flow rather than structural heart defects.

Increased blood flow across the pulmonic valve signifies that there is a higher volume of blood moving through this region compared to what is typically observed in older children or adults. This can occur in healthy infants as they transition from fetal to postnatal life, where pulmonary circulation is established. The sound associated with this increased blood flow is often a soft, systolic ejection murmur heard best at the left upper sternal border.

While conditions like closure of the ductus arteriosus, atrial septal defects, and ventricular septal defects can also lead to heart murmurs, they usually present with distinct clinical features and their murmurs may differ in quality or timing, reflecting underlying structural abnormalities rather than innocent flow-related murmurs. In this scenario, where the focus is solely on the primary cause of the detected murmur in an otherwise healthy infant during a routine examination, increased blood flow