See a Cardiologist to help answer this question. Your heart certainly does change from when one is 2 years old. Depending on the specific congenital heart abnormality, some people need multiple surgeries during childhood or into young adulthood, to account for the natural growing process that occurs.

Additionally, some valve replacements can wear out and the valves become "insufficient" or "leaky" over time. You don't say whether you have any cardiac or pulmonary symptoms.

At the very least, an Echocardiogram (Heart sonogram) should be done to look at your heart chambers and heart valves. Since a roller coaster can be a cardiologically stressful situation, they may wish to do an Exercise Stress Test to measure how your heart responds to physical stress.

Assuming your medical history, physical exam, and Echo and Stress Test turned out OK, there shouldn't be a contraindication to riding a roller coaster. However, if there is a problem--fluid or pressure buildup in parts of the heart, or a tendency to develop arrhythmias under physically stressful conditions, there could be problems with a roller coaster.

Speak to your Cardiologist first, and wait for his or her assessment before buying your next roller coaster ticket.