Sometimes a murmur may disclose an abnormality and sometimes a murmur has innocent implications. There is distinquishing sound as the blood passes through a heart valve and could indicate there is regurgitation (backflow of blood) of the mitral valve. Mitral valve is a one-way pass of blood from the upper chamber (receives blood from the lungs) to the lower chamber that pumps blood into circulation.
If the regurgitation is of medical consequences that would provide an abnormal EKG output. An EKG can show abnormal for reasons that aren't signficant and requires further testing or dismissed as not of any consequence because there are no findings or evidence to support a postive analysis for a medfical condition.
Usually murmurs are of no consequence and not unusual for a child to have an innocent murmu and it goes away.
Hope this provides a perspective, and if you have any further questions or comments you are welcome to respond, take care,
Ken