Left-to-right shunting may result in right heart enlargement and RV dysfunc- tion and, in a minority of patients, PAH. Some patients may have right-to-left shunting or paradoxical embo- lism, and some may develop arrhythmias. Percutaneous device or surgical closure are the mainstays of therapy in those with hemodynamic or clinical consequences of the defect. Severe PAH is a contraindication to closure, and its presence must be accurately excluded before ASD may occur with other congenital cardiac ab- normalities. In some circumstances, such as in patients with Ebstein anomaly and pulmonary stenosis (PS) or right HF, the physiology related to the ASD is substan- tially more complex, and ASD closure could result in clinical deterioration. Therefore, these recommenda- tions regarding ASD address only isolated ASDs and not ASD associated with complex CHD. Recommendations for Atrial Septal Defect (Continued) COR LOE Recommendations CLINICAL STATEMENTS AND GUIDELINES The Interventional Therapy Versus Medical Therapy for Secundum Atrial Septal Defect: A Systematic Review (Part 2) for the 2018 AHA/ACC Guideline for the Man- agement of Adults With Congenital Heart Disease S4.1.1-1 has additional data and analyses. The results from the question Are outcomes in asymptomatic patients with unoperated secundum ASD and RV dilatation improved after percutaneous or surgical closure? and the writing committee s review of the totality of the literature were used to frame decision-making. Recommendations that are based on a body of evidence that includes the sys- tematic review conducted by the ERC are denoted by the superscript SR (eg, LOE B-RSR ). 