To have a terminal disease is that you will eventually die from the disease if you do not have any interventions/surgeries. Here's the thing though. I also have heart disease
that is considered terminal although I plan on living a happy healthy life well into my 70s or 80s. I have had four heart surgeries and right now my doctors say I won't need another surgery until I am 40 (I am 19 right now). When I am 40 I will have another surgery, possibly a transplant and that could extend my life for about another 10 years and then I could either have more transplants or a mechanical heart. The thing is there are so many new surgeries and technologies that heart disease that could be termed terminal may not be terminal.
I suggest you talk to your parents. I regret that you had to come ask people on yahoo answers for that type of information as I am sure it will be very scary for you to learn this way.
If you need support there are two wonderful net communities. www.cchaforlife.orh (Canada) and www.achaheart.com (US) they will have even more people with these types of problems.