An atrial septal defect is a congenital heart defect where a hole exists in the wall separating the two upper chambers of the heart, the atria. This allows oxygen-rich blood from the left side of the heart to mix with oxygen-poor blood from the right side. This mixing of blood can lead to lower than normal oxygen levels in blood flowing to the brain, organs, and tissues. However, a small atrial septal defect may not produce noticeable symptoms. Multiplane transesophageal echocardiography can be used to image a moderate-sized atrial septal defect between the two atria.

2. Atrial septal defect (ASD) is a congenital
heart defect in which blood flows between
the atria (upper chambers) of the heart.
Normally, the atria are separated by a dividing
wall, the interatrial septum. If this septum is
defective or absent, then oxygen-rich blood can
flow directly from the left side of the heart to mix
with the oxygen-poor blood in the right side of
the heart, or vice versa.This can lead to lower-
than-normal oxygen levels in the arterial blood
that supplies the brain, organs, and tissues.
However, an ASD may not produce noticeable
signs or symptoms, especially if the defect is
small.

4. Multiplane transesophageal echocardiography showing a moderate-sized ostium
secundum ASD (1) in a 30° view. Ao indicates ascending aorta; LA, left atrium; and
RA, right atrium.

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