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Causes
By Mayo Clinic staff
Doctors know that heart defects present at birth (congenital) arise from errors early in the heart's development, but there's often no clear cause. Genetics and environmental factors may play a role.
An atrial septal defect allows freshly oxygenated blood to flow from the left upper chamber of the heart (left atrium) into the right upper chamber of the heart (right atrium). There it mixes with deoxygenated blood and is pumped to the lungs, even though it's already refreshed with oxygen. If the atrial septal defect is large, this extra blood volume can overfill the lungs and overwork the heart. If not treated, the right side of the heart eventually enlarges and weakens. In some cases, the blood pressure in your lungs increases as well, leading to pulmonary hypertension.
Comparing ASD with patent foramen ovale
The term "atrial septal defect" usually refers to holes in the atria resulting from a lack of atrial septal tissue, rather than those related to a condition called patent foramen ovale (PFO).
Patent foramen ovale occurs when part of the normal fetal heart circulation fails to close properly at birth. During fetal heart development, a channel (the foramen ovale) is present between the atria to allow blood to bypass the lungs. At birth, once the lungs take over breathing, the hole normally closes. In about one in three people, this opening doesn't close.
