The ostium primum atrial septal defect is a defect in the atrial septum at the level of the tricuspid and mitral valves.
[en.wikipedia.org]
The ostium primum atrial septal defect is seen in the apical four chamber view as a lack of substance in the inferior part of the atrial septum.
[symptoma.com]
Defects, Atrial, ATRIAL SEPTAL DEFECT, Defect, Atrial Septal, Defects, Atrial Septal, HEART SEPTAL DEFECT ATRIAL, IA SEPTAL DEFECT, SEPTAL DEFECT INTERATRIAL, Septal Defect
[fpnotebook.com]