Heart murmur ..any thing serious?

Question is unclear: A murmur is a type of heart sound the doctor can hear with a stethoscope. Whether nor not a murmur is a birth defect depends on the cause of the sound. If the sound is caused by incorrectly formed arteries, veins, or heart parts, then the problem is a birth defect. On the other hand, many normal children have murmurs but no defects (the murmurs are probably just from the flow of the blood).