thanks for posting,
Given the fact that you have had a previous surgery especially one that involves the heart. I advise you proceed with care and you may only involve physical activity upon advise of your doctor. You will need your heart evaluated completely with stress
tests done to evaluate your heart's condition before you can go on a roller coaster. Your situation might be much more delicate than you can feel it and it is advisable to consult with a cardiologist first.
Hope this helps