ASD is the most common congenital cardiac anomaly.
Types:
-Ostium secundum: most common type (60%)
-Ostium primum (35%)
-Sinus venosus defect, at entrance of SVC (5%)

Associations:
-Holt-Oram syndrome: secundum defect
-Lutembacher syndrome: ASD and mitral stenosis
-Down syndrome: primum defect

Clinical findings:
-may be asymptomatic for decades
-low pressure defect better tolerated than VSD or PDA
-Female preponderance
-May present with pulmonary hypertension