This is a congenital condition which is commonly diagnosed in adulthood. There is an increased incidence in females.
The communication between the atria allows left-to-right shunting of blood. The low pulmonary vascular resistance and the distensibility of the right ventricle leads to an increase in right heart output.
After the age of about 30 years old there may be an increase in vascular resistance which can give rise to pulmonary hypertension. Atrial fibrillation may then be seen.