Tom,
You must do what the Dr. says.
I have had 2 open heart surgeries. Now I have a artificial aortic valve and a pace maker/defibulator. I've never felt better.
Every time Donny sees me heading to the line, he shakes his head. I know that he is wondering if today is the day. lol
My Dr. said no more racing dirt bikes, because of the fact that when you go to slow you tend to tip over and end up all bruised up. ( Because of the blood thinners )
So I convinced him that quads would be much safer, because of 4 wheels, and they must be more stabile. He has never seen a quad race and agreed to my madness. That was in the beginning of 2012.
The only thing that I can tell you is please don't ride over your head. And remember that every time you get to race it's a blessing. Have fun!!!
I do still have a 2 wheeled race bike, but I feel that I feel safer on my quad. Probably a false sense of security. I just will not take any chances, its just not worth it.
While on vacation, a couple of years ago, I rolled my wife's quad. This resulted in a tear at my adrenal glad and kidney, and knocked some gall stones loose. This caused for a lot of pain, ALOT of bruising from internal bleeding, and quite a few days in the hospital. The Dr's were scared mostly because of the blood thinners.
Just use your sense and try to remember why we do this. It's fun and all of our friends are there.