Safety and Efficacy Study of reSept ASD Occluder for Treating Secundum ASD

Inclusion Criteria: All responses must be Yes to be eligible: 1. Age \< 85 years. 2. Body weight ≥ 15 kg / 33 lb. 3. Males and Females. 4. Clinically significant, isolated secundum ASD associated with a L-R shunt and signs of RV volume overload that, based upon the expertise of attending physicians requires treatment. 5. ASD of size 5 to 19 mm on screening diagnostic echocardiogram. 6. Isolated secundum ASD of size 8 to 22 mm on stop flow balloon diameter, based upon echocardiographic and fluoroscopic evidence obtained at procedure. 7. Able to take required medications: ASA (Aspirin), low dose (75-100 mg/day), 24 hours prior to and for 6 months following the procedure; Heparin intra-procedurally. 8. Adequate septal rim to support the device. The rim is considered inadequate if it measures less than 5mm in more than two views of a critical structure 9. Adequate defect margin to safely accommodate the selected size implant without interfering with adjacent cardiac structures (e.g., aorta, AV valves, ostia of the pulmonary veins, coronary sinus, or other critical structures), based on the IFU sizing guidance. 10. Capable of giving informed consent, or, for minors, consent of the parent or legal guardian, and willing to comply with the clinical investigation requirements. Exclusion Criteria: All responses must be No to be eligible: 1. Pregnancy. Females with child-bearing potential are required to be tested for pregnancy prior to treatment, in accordance with the local institution's policy. For minor females, a pregnancy test will be done in accordance with the local institution's policy. 2. Any significant valve dysfunction that contraindicates ASD closure, or increased pulmonary vascular resistance/severe pulmonary hypertension. 3. Acquired pathological or congenital abnormalities of the cardiovascular system (other than isolated secundum ASD; e.g. congenital malformations, calcification, myocardial infarction, intracardiac thrombi, dilated cardiomyopathy, untreated coronary disease or CAD treated with a stent in the prior 12 months) being clinically significant, that would interfere with the conduct of the clinical investigation. 4. Subjects having undergone left sided structural heart interventions performed via transseptal access (e.g. Mitraclip, LAAO, percutaneous mitral valve replacement). 5. Evidence of thrombus in the left atrium, left atrial appendage, other cardiac chamber, or the inferior vena cava. 6. Sepsis or any other infection that was not successfully treated at least 30 days prior to device placement. 7. Active endocarditis or other infection(s) producing bacteremia. 8. History of atrial tachycardia, atrial fibrillation or flutter, AV block, or ventricular arrhythmia requiring antiarrhythmic medication, pacemaker or AICD. 9. Vasculature is of inadequate size to accommodate all procedural instrumentation. 10. Known allergy to investigational device components or medications, or other contraindication to clinical investigation medications (acetylsalicylic acid, heparin), including a documented history of bleeding, clotting or coagulation disorders, untreated ulcer or any other contraindications to acetylsalicylic acid or antiplatelet therapy. 11. Known hypercoagulable state. 12. Any disorder in the investigator's opinion that could interfere with compliance of safety evaluation as well as any severe concurrent illness that would limit life expectancy (e.g. malignancies). 13. Currently an active subject in an investigational drug or device study that could confound the results of this study. 14. Patients who, in the opinion of the investigator, are inappropriate for inclusion into this clinical investigation or will not comply with requirements of the clinical investigation. 15. Are known to abuse drugs or alcohol. 16. Patients with the diagnosis of Patent Foramen Ovale (PFO).