Undiagnosed Atrial Septal Defect in the Setting of Comorbidities and Ventricular Failure: Seemingly Simple Disease with a Challenging Diagnosis.

• In adults, ASD remains underdiagnosed, particularly in the setting of comorbidities. • A high index of suspicion is needed to find ASD in PH and/or ventricular dysfunction. • Multiple views, including subcostal view, and ASC injection improve ASD diagnosis. • Multimodality imaging is essential with nondiagnostic TTE and suspected CHD.