My son has atrial septal defect with aortic insufficiency. how serious is this?

Depends on severity: If the atrial septal defect is large enough that it is causing enlargement of the heart's rt side he needs to have it closed either with surgery or more likely with one of several types of devices done in the cath lab with no scar. As for the aortic insufficiency, this will depend on the severity; mild degrees can be followed, moderate to severe may need medications or intervention. See your doc.