A patent foramen ovale (PFO) is a hole in the heart that didn't close the way it should after birth. The hole is a small flaplike opening between the upper heart chambers. The upper chambers of the heart are called the atria.

As a baby grows in the womb, an opening called the foramen ovale (foh-RAY-mun oh-VAY-lee) sits between the upper heart chambers. It typically closes during infancy. When the foramen ovale doesn't close, it's called a patent foramen ovale.

Most people never need treatment for patent foramen ovale.


Patent foramen ovale occurs in about 1 in 4 people. Most people with the condition never know they have it. A patent foramen ovale is often discovered during tests for other health problems.


It's unclear why the foramen ovale stays open in some people. Genetics may play a role.

How the heart works

To understand more about patent foramen ovale, it may be helpful to know how the heart typically works.

The typical heart has four chambers that pump blood:

  • The right upper chamber, also called the right atrium. This heart chamber receives oxygen-poor blood from the body. It pumps blood to the right lower heart chamber through the tricuspid valve.
  • The right lower chamber, also called the right ventricle. This heart chamber pumps blood to the lungs through a large vessel called the pulmonary artery. In the lungs, blood picks up oxygen. The blood moves through the pulmonary valve. The valve closes when the chamber relaxes between beats.
  • The left upper chamber, also called the left atrium. This heart chamber receives the oxygen-rich blood from the lungs. It sends blood through the pulmonary veins and mitral valve and into the left lower chamber.
  • The left lower chamber, also called the left ventricle. This chamber is the heart's main pumping chamber. It pumps the oxygen-rich blood to the rest of the body through the body's largest blood vessel, called the aorta. The blood passes through the aortic valve, which also closes when the chamber relaxes.

The heart before birth

Because a baby in the womb isn't breathing, the lungs aren't working yet. That means there's no need to pump blood to the lungs. At this stage, blood goes around the baby's lungs. It uses the placenta and umbilical cord to move oxygen-rich blood from the mother to the baby's body.

In the baby's body, blood vessels connect to the umbilical cord. Oxygen-rich blood gets to the heart through the vein that drains blood from the body to the right upper heart chamber. This vein is called the inferior vena cava. The blood then goes across the foramen ovale and into the left upper heart chamber. Finally, the blood enters the left lower heart chamber, which pumps it throughout the body.

Newborn baby's heart

When a baby's lungs begin working, blood flow through the heart changes. Now the oxygen-rich blood comes from the lungs and enters the left upper heart chamber.

The pressure of the blood pumping through the heart usually forces the flap opening of the foramen ovale to close. In most people, the opening closes sometime during infancy.


A patent foramen ovale, also called a patent foramen ovale (PFO) usually doesn't cause complications. Some people with a PFO may have other heart defects

Possible complications of patent foramen ovale may include:

  • Low blood oxygen. Rarely, a patent foramen ovale can cause a significant amount of blood to go around the lungs. This lowers blood oxygen levels, a condition called hypoxemia.
  • Stroke. Sometimes small blood clots in veins may travel to the heart. They may go through a patent foramen ovale and into the left side of the heart. From there, they can travel to the brain and block blood flow, causing an ischemic stroke.

Some studies have found that patent foramen ovales (PFOs) are more common in people with unexplained strokes and migraines with aura. But more research is needed. Usually, there are other reasons for these conditions. It's often just a coincidence a person also has a PFO.