Hello,
I am very sorry to read this. I understand how devastating news like this can be, especially when you are not expecting it.
It sounds like they do not perceive an immediate risk to your child, which I think is very good. Anticipating the possible need for a procedure, I would schedule a second opinion now. I I am not sure where your first opinion is from, but consider looking for a reputable pediatric cardiology program and obtaining a second opinion. It can't hurt and will only help keep you more informed. I would try to find out if this problem has a name (congenital aortic stenosis, unicuspid aoritic valve, etc.)--atleast that would make it easier for you to become informed parents and do some research.
I have not been a physician for children since medical school, so that is the best I can offer for now.
I hope this helps and good luck.
Please take a look at ValveReplacement.com where you'll "meet" caring people who've had a child go through valve replacement, or have gone through the experience themselves. It's a small, wonderful community where I hope you'll find answers and support.
Blessings,
Carolina
Best wishes
Jim