Spontaneous Closure of a Secundum Atrial Septal Defect.

Spontaneous closure of an atrial septal defect (ASD) is well described in pediatric cardiology but may be less familiar to adult internists and cardiologists. We report a moderately sized 6-mm ASD that closed spontaneously without intervention. A literature review found that a smaller defect size and an early age of diagnosis are the most important predictors of closure. Possible mechanisms of a spontaneous ASD closure include adaptive endothelial migration, limited myocardial proliferation, and fibroblast migration with extracellular matrix deposition.