P.,
Coming from an entire family with heart murmurs of different types (my father, my brother, myself and my daughter), I can tell you that, although initially frightening, the murmur is really nothing to get too worried about. I myself have lived with one without problem for 35 years. It really depends on what type of heart murmur your child has. I have a tricuspid valve regurgitation and taking an antibiotic before surgeries or dental appointments and the occasional 'hiccup' in my chest are the only effects it has had on my life. My daughter and brother, however, both were diagnosed with PDA - patent ductus arteriosis which is commonly known as a 'hole in the heart'. This is a condition that cardiologists reccomend gets corrected. I know people who have lived with this condition their whole lives without problem but there is risk for endocarditis when it is left untreated. My daughter was diagnosed at around 6 months of age. Her pediatrician detected a murmur and determined that it needed to be checked out by a cardiologist. The cardiologist performed an ultrasound. (Just like you had on your abdomen while you were pregnant). It's not uncomfortable for the baby, just some cold jelly on his chest. My daughter's cardiologist determined, from that ultrasound, that she did have PDA and the surgery was performed only a few weeks later. The chance of your son having this condition just because he has a murmur is rare but, if he did, I can tell you that the surgery is just an outpatient procedure and lasts only about a half hour. It's a procedure performed like a heart catheterization. It was scary for me but my daughter went home within a few hours of the surgery and had no pain or recovery issues.
My recommendation is, as far as your doctor is concerned, question him as soon as you can about whether or not he feels your son might have a murmur associated with patent ductus arteriosis. If he sounds certain that it definitely is not. I would go with that diagnosis but find out what type of murmur it is. Every doctor, dentist, whatever he sees for the rest of his life will need to know this. If your doctor is unsure of what type of murmur it is, don't let him put it off, I would ask to be referred to a pediatric cardiologist, just to be certain. If indeed it was PDA, the corrective surgery is easiest on a small child as the catheter hasn't as far to travel and small children are (especially those in daycare) more at risk to types of illnesses that can pose the greatest threat to a vulnerable heart.
I hope my insight has been helpful to you. If you need any other advice on this subject, please feel free to email me. ____@____.com.