atrial septal defect 3 (MONDO_0013567) is any atrial heart septal defect in which the cause of the disease is a mutation in the MYH6 gene. Also known as: ASD3, MYH6 atrial heart septal defect, atrial heart septal defect caused by mutation in MYH6, atrial heart septal defect type 3, atrial septal defect type 3.