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Causes
By Mayo Clinic staff
An overview of normal heart function in a child or adult is helpful in understanding the role of the foramen ovale before birth.
Normal heart function
Your heart has four pumping chambers that circulate your blood:
- The right atrium, the upper right chamber, receives oxygen-poor blood from your body and pumps it into the right ventricle.
- The right ventricle, the lower right chamber, pumps the blood through a large vessel called the pulmonary artery and into the lungs, where the blood is resupplied with oxygen and carbon dioxide is removed from the blood.
- The left atrium, the upper left chamber, receives the oxygen-rich blood from the lungs and pumps it into the left ventricle.
- The left ventricle, the lower left chamber, pumps the oxygen-rich blood through a large vessel called the aorta and on to the rest of the body.
Baby's heart in the womb
Because a baby in the womb isn't breathing, the lungs aren't functioning yet. The heart needs to bypass the lungs and use a different route to circulate oxygen-rich blood to the body.
The umbilical cord delivers oxygen rich-blood to the baby's right atrium. Most of this blood travels through the foramen ovale and into the left atrium. From there the blood goes to the left ventricle, which pumps it throughout the body. Blood also travels from the right atrium to the right ventricle, which also pumps blood to the body via another bypass system.
Newborn baby's heart
When a baby's lungs begin functioning, the circulation through the heart changes. Now the oxygen-rich blood comes from the lungs and enters the left atrium. At this point, blood circulation follows the normal circulatory route.
The pressure of the blood is generally greater in the left atrium than in the right atrium. This pressure forces the foramen ovale closed. In most people, the opening fuses shut, usually sometime within the first or second year of life.
In people with other congenital heart defects, the foramen often doesn't close. It's unclear why the opening never closes in other people, but genetic factors may play a role.
