A heart murmur is a very common condition. Many people have these -- some of which are serious and require treatment, some of which are minor and even go away on their own. I would recommend that your nephew see his doctor
for further evaluation.
A heart murmur occurs when blood flows in the heart in a turbulent fashion. Normally, blood flows smoothly and quietly, but if there is something that makes the blood turbulent -- a murmur can be heard. The most common cause of a murmur in young people is simply what we call a "flow murmur." This means that the heart is just working hard to pump blood that the blood sounds turbulent. This often goes away on its own. Another cause of the abnormal flow is if there is a problem with the valve -- either it is too small or too floppy. This can be a problem and this can require treatment. A third possibility (there are others but these three are the big one) is that there is a small hole in the heart and that blood is flowing in the wrong direction.
If there is a hole in the heart or a severely damaged valve -- this can lead to problems with the heart pumping and can (without treatment) be fatal.
of the heart can often be done to see exactly what is causing the murmur. Again, please talk to his doctor for more information.