Safety and Efficacy Study of Transcatheter Closure of Ostium Secundum ASDs

Inclusion Criteria: All responses must be Yes to be eligible: 1. Patient has an ostium secundum ASD with evidence of left-to-right shunt and right ventricular volume overload. 2. Patient has a defect size 8-35 mm as measured directly by stop-flow balloon sizing. 3. Patient vasculature can accommodate the delivery system and procedural accessories. 4. Patient can accommodate TEE or intracardiac echocardiography (ICE) probe for implant procedure. 5. Patient is judged by the implanting physician to have adequate septal rims to retain the study device. 6. Patient (or legal guardian, if patient is a minor) will voluntarily sign a Patient Informed Consent Form (ICF) specific to the study. The Patient ICF must be reviewed and approved in a manner that complies with requirements of the hospital's Institutional Review Board (IRB). 7. Patient (and legal guardian, if patient is a minor) is physically and mentally willing to comply with all study follow-up requirements through 36 months, including routinely scheduled diagnostic testing and physical examinations. Exclusion Criteria: All responses must be No to be eligible: 1. Patient has significant known pre-existing electrophysiologic or structural cardiovascular defect, or other comorbidities that could elevate morbidity or mortality beyond what is common for ASD or would require surgical treatment within three (3) years of device placement. Examples include, but are not limited to, large ventricular septal defect, hypoplastic left heart syndrome, coarctation, univentricular heart or tricuspid atresia, pulmonary hypertension, coronary artery disease, valvular or myocardial dysfunction, and other congenital heart disease requiring surgical repair. 2. Patient has systemic or inherited conditions that would significantly increase risk of major morbidity and mortality during the term of the study. Examples include endocarditis, cancer, degenerative neuromuscular disorder, cardiomyopathy, and any condition expected to result in significant deterioration of health within three (3) years of the index procedure. 3. Patient has anatomy where the size or position of the occluder would interfere with other intracardiac or intravasculature structures, such as cardiac valves or pulmonary veins. 4. Patient has active endocarditis, other infections producing bacteremia, or has known sepsis within one month of planned implantation, or any other infection that cannot be treated successfully prior to device placement. 5. Patient has known intracardiac thrombi. 6. Patient has an uncontrolled arrhythmia with evidence of arrhythmia control failure within the past 90 days (e.g., supraventricular tachycardia while under rate control or atrial fibrillation while under rhythm control) or requires electrophysiology study or concomitant intervention with device placement. 7. Patient is awaiting a procedure that requires trans-septal left atrial access within 6 months of implant procedure. 8. Patient has a history of stroke resulting in a significant morbidity or disability. 9. Patient is pregnant or lactating at time of screening. 10. Patient has contraindication to antiplatelet and anticoagulant medications. 11. Patient has elevated pulmonary vascular resistance (PVR) which in the opinion of the implanting physician precludes safe defect closure. 12. Patient has multiple defects based on screening imaging and stop-flow balloon sizing that would require placement of more than one device.