I would have to agree with medic58. I would ask your doctor why it is he feels it's not a good idea, obviously I have no idea what your medical history is. I do know there is a very small chance of getting pericarditis with piercings if you have certain heart issues. I myself have a bicuspid aortic valve (along with other issues), therefore I have to take antibiotics before dental work and other such things and I've read piercings can be an issue. BUT I have my tongue, navel and nose all pierced. I had them done before I knew about my heart issues and I've never had any issues. I would think that as long as you go to a place where the piercing is done properly that you would be fine, maybe you could even get a prophylactic antibiotic from your doctor before hand.. Definitely discuss it with your doctor and see what he might be able to do for you.
If I was you I would ask my Dr. why it would be bad for my heart. I would think that most piercings are very safe and the threat of infections low (as long as everything is sterile and proper care is taken of the site). Of course that is a decision that you and your parents along with your Dr. need to make...