If i had asd surgery when i was a baby what would cause heart pain now after 18 years?

Probably not heart: Most 18 year olds most likely are not going to have "heart pain" as you put it. If you're having palpitations and rapid heart beat, that can feel unusual and should be checked. However most likely the pain is when you breathe, or right in the middle of the chest, and represents pain where the cartilage meets the sternum. Get this looked at, but a muscular problem sounds more likely.

Not likely: While you can have chest pain from a surgical incision, it is unlikely that you would be getting cardiac pain this far away from your surgery. Look for other causes.

Many Things: There are many potential causes of chest pain. People who've undergone heart surgery are at risk for heart rhythm problems. Also at risk, though not likely with just an asd, for residual problems in the heart. And everyone is at risk for coronary artery disease. Please see a doctor to evaluate this as chest pain can be serious.