my dd1 is 5 and they have just detected a heart murmur
she has been referred to the cardiology dept and what my gp said they will do is some ultrasound scans - like the ones you get when you are pg - of her heart, and possibly and ECG or an ECHO which is like an ECG
does he have any other symptoms? breathlessness, blue lips? if not then it could be what they call an 'innocent' murmur and your ds could quite possilbly grow out of it or that it will just be 'there' and he will not suffer at all
Lots of children have them, and the majority do turn out to be innocent - not caused by anything which will ever cause them a problem, just a little extra sound which doesn't signify anything.
My DS had one detected at his 3 year check, and had various tests, but it turned out to be innocent.
He had blood tests, a chest x-ray, and then an ultrasound. The blood tests show whether the heart is having to work harder than it should be, which would be a sign there is a problem. The x-ray would have showed if the heart was enlarged, which again shows it has a problem and is having to work harder.
The ultrasound, as nailpolish says, is to look for problems with the heart valves. If the murmur is caused by a problem, it would most likely be one of the valves not opening or closing as well as it should.
As other have said, lots of children have them, and if you weren't worried about any symptoms before the checkup (not growing well, listless etc) then there is a good chance it is innocent and won't need anything done.