A Patent Foramen Ovale, or PFO, is an opening between the right and left atriaThe atria are the two upper chambers of the heart. They act as reservoirs for blood that will fill the ventricles. of the heart. This type of atrial communication is commonly referred to as an ASD (Atrial Septal Defect). It is a remnant of fetal life, present in about 25% of the population.
The Human Heart
The heart is divided into four distinct chambers, separated by tight walls called septa, and valves that guide bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood flow in the right direction.
You can think of it like a house with several rooms and doors that allow movement from one to another.
Heart Development
The heart starts to form within the first few weeks of embryonic life. At first, it looks like a simple tube with narrow and wide segments.
It initially includes a single atrium (called the primitive atrium) and a single ventricle (primitive ventricle).
Formation of the Atrial Septum
Over time, the primitive atrium divides into two parts: the right atrium and the left atrium. This separation happens as a wall, called the atrial septum, forms.
This septum doesn’t form all at once. It develops in two steps, creating two separate layers.
Two Layers
The first layer forms with a central opening. Then, a second layer appears, with its own opening located slightly lower. This second opening has an oval shape—hence the name “foramen ovale.”
In the fetus, these two layers are not fully sealed, allowing bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood to flow freely between the two atriaThe atria are the two upper chambers of the heart. They act as reservoirs for blood that will fill the ventricles..
A Normal Communication in the Fetus
During fetal life, this communication between the two atriaThe atria are the two upper chambers of the heart. They act as reservoirs for blood that will fill the ventricles. is completely normal. It allows bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood to bypass the lungs, which are not yet functional at this stage. Only a small amount of bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood reaches the lungs—just enough to support their development.
Gas exchange doesn’t take place in the lungs but through the placenta. That’s where oxygen is absorbed and waste products are eliminated.
Most of the bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood that enters the right atrium crosses over to the left atrium by passing first through an opening called the ostium secundum, then through the space between the two layers of the septum, and finally exits into the left atrium via the foramen ovale.
This oxygen-rich bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood is then pumped out by the left ventricle to nourish the developing fetus.
See also: Atrial development
At Birth, the Communication Closes
At birth, the lungs expand and begin to function. BloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood can now flow through them freely to collect oxygen. As this pulmonary circulation becomes easier, the pressure in the right atrium naturally decreases.
The pressure in the left atrium then becomes higher than in the right. This difference pushes the two layers of the septum against each other, effectively closing the temporary “tunnel” between the atriaThe atria are the two upper chambers of the heart. They act as reservoirs for blood that will fill the ventricles..
According to some studies, about 75% of these fetal atrial communications close completely within the first few months of life. When this doesn’t happen, it’s called a patent foramen ovale (PFO).
What Does This Actually Mean?
After birth, bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood flows through a well-defined path involving the heart, lungs, and bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood vessels, with no backward flow. But when a patent foramen ovale (PFO) is present, a small opening remains between the two atriaThe atria are the two upper chambers of the heart. They act as reservoirs for blood that will fill the ventricles.. This means that a small amount of bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood can still cross from one atrium to the other.
This passage remains minimal and, in most cases, has no effect on how the heart functions.
However, a reverse flow is also possible: bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood may sometimes move from the right atrium to the left. This is known as a paradoxical shunt, because it goes against the usual direction of bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood flow.
Paradoxical Embolism
When a small blood clot crosses through a patent foramen ovale (PFO) and reaches the left side of the heart, it can then be propelled into the arterial circulation.
If it travels toward the brain, it can block a vessel and cause a transient ischemic attack (TIA) or, in more serious cases, a stroke (cerebrovascular accident, or CVA).
This type of embolism is called paradoxical because the clot originates from the right side of the heart but takes an unusual shortcut to the left, bypassing the lungs, which would normally filter it out. While this situation is rare, its consequences can be significant.
What Are the Possible Symptoms?
It is estimated that around 25% of the population has a PFO. In the vast majority of cases, this anatomical feature causes no symptoms at all.
Some researchers have suggested a possible link between PFO and migraine headaches, but this association remains poorly understood and unproven. In reality, the only symptoms that might be linked to a PFO are neurological in nature, and usually occur after a stroke or a transient ischemic attack (TIA).
When such an event occurs, a series of tests is conducted to determine the cause. If no clear explanation is found and a PFO is detected, it may be suspected as a contributing factor.
It is worth noting that about half of patients who suffer a stroke or TIA with no identifiable cause are found to have a PFO. This suggests a possible link… but the other half of these patients do not have a PFO and still experience the same kind of brain event. That makes it harder to draw definitive conclusions.
For this reason, the diagnosis is often one of exclusion, especially in people under age 50 and in otherwise good health, for whom no other cause of stroke can be identified.
How Can a Patent Foramen Ovale (PFO) Be Detected?
Unlike some congenital heart defects — such as a true atrial septal defect (ASD) — a PFO does not produce a detectable heart murmur. This means it often goes unnoticed during a routine physical exam.
In many cases, it is discovered incidentally, during a cardiac ultrasound (echocardiogram) ordered for another reason. Even then, it will only be detected if the medical team is specifically looking for it.
A trick using microbubbles
Cardiac ultrasound specialists have a well-practiced method to detect a PFO: they use microbubbles.
The principle is simple. Imagine shaking a bottle of water — it turns cloudy because of tiny bubbles. Doctors reproduce this effect by injecting a mixture of saline and air into a vein in the arm. This creates small bubbles that are visible on ultrasound.
In a person without a PFO, these bubbles travel to the lungs, where they are naturally filtered. They should never appear in the left side of the heart.
But if microbubbles are seen in the left atrium shortly after injection, it means they’ve crossed the septum — a sign that a PFO is present.
Transesophageal echocardiography: a more precise test
A transthoracic echocardiogram (TTE), done with a probe placed on the chest, is often the first test performed. However, it may not always be accurate enough to detect a small PFO or provide clear images.
In that case, a more detailed test may be used: transesophageal echocardiography (TEE). With this test, the ultrasound probe is inserted into the esophagus, similar to a gastroscopy. Since the esophagus runs just behind the heart, the probe can capture much sharper images.
This makes it possible to confirm the presence of a PFO and better understand its shape and size. The exam is usually done under light sedation and is well tolerated.
Read more: Transesophageal echocardiography (TEE)
What should be done if a PFO is found?
Discovering a patent foramen ovale (PFO) often raises an important question: should anything be done? The answer depends on the context.
-If there are no symptoms
If there are no symptoms or neurological events (such as a stroke or TIA), no treatment is needed. Many people live their entire lives with a PFO without ever knowing it—and without any issues.
-If there has been a stroke or TIA
Things become more complex when a PFO is discovered after a stroke or a transient ischemic attack (TIA), especially in people under the age of 60.
In this context, treatment to reduce the risk of clot formation is often recommended. It may involve:
- an antiplatelet drug (such as aspirin),
- or an anticoagulant (such as warfarin or direct oral anticoagulants, known as DOACs).
Can someone live normally with a PFO?
Yes. In the vast majority of cases, people with a PFO can lead a completely normal life, including physical activity, travel, and—if applicable—pregnancy.
Should antibiotics be taken before dental or surgical procedures?
No. Unlike certain other heart conditions, a PFO does not require preventive antibiotics before procedures. However, good oral hygiene is always recommended.
Read more: Preventing endocarditis
Closing the PFO: a shared decision
Closing the PFO is sometimes considered, especially in young patients who have had a stroke with no other apparent cause.
This decision is made in collaboration with a neurologist and a specialized cardiologist.
The procedure is non-surgical and involves closing the PFO with a small device inserted through a catheter.
Before the intervention, the patient meets with the medical team to review the procedure, the expected benefits, and potential risks. This choice is always personalized, based on individual health and medical history.
Read more: Percutaneous closure of PFO
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