Ostium secundum atrial septal defects present as a persistent communication between the atria and are a common congenital cardiac anomaly accounting for approximately 10% of all congenital heart disease. They are one of the most common congenital heart defects to present in adulthood. Untreated, ASDs produce right heart volume overload and progressive impairment over time, including reduced aerobic capacity, atrial dysrhythmias, congestive heart failure, pulmonary hypertension, and potential paradoxical embolism. In the U.S. alone it is estimated that approximately 10,000 new patients per year can be expected to have an ASD. Successful surgical repair of ASD has been performed for 50 years with continued improvement in technique and outcomes. King and Mills reported the first transcatheter closure of ASD in 1976, but the delivery system was quite large and impractical, especially for younger patients. With time, improvements in design concepts and materials discoveries have led to improved results in transcatheter closure systems. Several devices are now available commercially for transcatheter ASD closure.