The first successful transcatheter closure of an ASD was performed by King and Mills in 1974. The device was composed of two opposing umbrellas and required a 23 Fr introducer. Since then different device designs have been studied. There are now two FDA-approved devices used for ASD closure: AMPLATZER Septal Occluder® and Helex®. Secundum atrial septal defects are usually closed to reduce right ventricular volume overload (RVVO) which is diagnosed by echo or MRI. In the presence of RVVO by noninvasive measures the ASD meets indication for closure, even when the measured Qp/Qs in the lab may suggest a less than 2:1 shunt. However, occasional patients get to the lab with a misdiagnosis or missed diagnosis, e.g., the TEE shows intact septum, multiple defects, or there are pulmonary venous anomalies, which may make ASD closure inappropriate.