Wow, you've had a rough couple of weeks. Glad you're on the mend. A few things:
1) Problems with the aorta are among the most serious medical problems that people can have. If it does rupture, the prognosis is not good.
2) Follow your cardiologist's orders to the letter. With the issue of roller coasters, he may just not know and would prefer to err on the side of caution. There is almost *zero* medical research on how coasters affect the human body. I think there have been like 2 studies in the last 20 years or something, according to an article I read in JAMA not too long ago.
http://www.or-live.com/HealthEast/1449/ ... ebcast.cfm
At about 45:30 someone asks if brain aneurysm patients should avoid roller coasters. But they're talking about brain aneurysms, NOT aortic aneurysms. The aorta is under a lot more pressure than any other blood vessel, so the rules might be different.
If I were you, I'd just err on the side of caution and avoid coasters for the time being.