My son was born w/ ASV and VSD. (2 holes) They noticed this immediately at the hospital and did an Echocardiogram before we left. If they are just now hearing this the hole it is probably really small. My doctor said it is very common and majority of kids grow out of it or live with it and have no limitations.
At the cardiologist appt. they will do an ecocardiogram, which is basically an ultrasound...non-invasive and they can measure how big it is. They will probably do an EKG as well. Totally all non-invasive stuff. Take a bottle and let him be just a little hungry. They need to be really still for the ecocardiogram and feeding is the easiest way.
My son later developed Pulmonic Stenosis (narrowing of the Pulmonary Valve), but the holes have slowly been getting smaller (one has acutally closed already).
I wouldn't let it get you upset because you will find out when you go to the Cardiologist that you are blessed to have a son in such good condition (there are so many sick babies)!!!
I understand the concern, make the appointment, get it checked out and you'll fell better!
If your son does have VSD the only difference between him and other kids is that he will probably have to have a shot of antibiotics before any surgeries, dental work, ect.. for infection purposes.
I assure you that if this was really bad, he would have failure to thrive (eating problems, low weight, lathargic, ect..) that would have showed up by now!!
I would just pray of the murmur to be healed and thank God for giving you such a beautiful baby boy!!