Understanding Patent Foramen Ovale (PFO) and Stroke Risk

Kristian Doyle
Nov 5
5 min read

A patent foramen ovale (PFO) is a small flap-like opening between the upper chambers of the heart that normally seals soon after birth. For roughly one in four adults, it remains open. In most cases this doesn’t cause any symptoms and goes unnoticed for life. Yet for some people, especially those who have had a stroke with no clear cause, a PFO can take on new importance.

This article explains how a PFO might increase stroke risk, how doctors test for it, including the role of the transesophageal echocardiogram (TEE), and what treatment options are available to prevent another stroke.

What Is a Patent Foramen Ovale?

Before birth, the foramen ovale serves as a natural passageway that allows blood to bypass the lungs, which are not yet functioning. After birth, as the lungs begin to supply oxygen, the opening is supposed to close. When it does not, the flap can stay open and permit blood to flow between the right and left sides of the heart.

In most people this tiny opening is harmless. Blood pressure on the left side of the heart is usually higher than on the right, which keeps the flap closed most of the time. But when pressure shifts, such as during coughing, straining, or heavy exertion, blood can momentarily pass from the right atrium to the left. If a small blood clot happens to be circulating at that moment, it can travel through the PFO, reach the arteries, and lodge in the brain, causing an ischemic stroke. This process is called paradoxical embolism.

How a PFO Can Contribute to Stroke

The link between PFO and stroke has been studied for decades. Most strokes are caused by traditional risk factors such as atherosclerosis, high blood pressure, or atrial fibrillation. But in a subset of younger adults who experience what’s called a cryptogenic stroke, a stroke with no identifiable cause even after extensive testing, a PFO may be the culprit.

The risk that a PFO contributes to stroke depends on its anatomy and function. Larger openings that allow more blood to pass through, or those associated with an atrial septal aneurysm (a flexible bulge in the heart wall), tend to be more concerning. People who have blood clotting disorders or a history of deep vein thrombosis also face a higher risk because they are more likely to form clots that could travel through the PFO.

It’s important to emphasize that not all PFOs are dangerous. Many are small and never cause problems. The challenge for clinicians is determining whether a PFO found on imaging is simply a coincidence or actually the pathway that allowed a stroke to occur.

How a PFO Is Diagnosed

Doctors use several imaging techniques to detect a patent foramen ovale (PFO) and evaluate how much blood may be passing through it. The first step is often a transthoracic echocardiogram (TTE), an ultrasound performed on the chest that can reveal larger openings but may miss smaller ones.

If results are unclear, doctors may use a transcranial Doppler (TCD), which tracks the movement of tiny air bubbles in the brain’s blood vessels after a saline injection. Seeing bubbles appear in the arteries suggests that blood has crossed from the right to the left side of the heart, a sign of a PFO or similar shunt.

For the most detailed view, a transesophageal echocardiogram (TEE) is often performed. In this procedure, a flexible probe is guided down the esophagus, directly behind the heart, to capture high-resolution images of the thin wall separating the heart’s upper chambers. During the test, doctors usually perform a “bubble study,” injecting saline mixed with microbubbles into a vein while the patient briefly strains. If bubbles appear in the left atrium, it confirms that blood, and potentially clots, can pass through the PFO.

Although TEE requires mild sedation and is more invasive than a standard echocardiogram, it provides the most complete information about the PFO’s size, shape, and movement. These details help physicians determine whether the opening could have contributed to a stroke and guide decisions about whether closure might be beneficial.

When Is PFO Closure Considered?

Discovering a PFO doesn’t automatically mean it should be closed. Most people with a PFO will never experience a stroke, and for many, the risks of closure outweigh the benefits. However, in people who have had a cryptogenic stroke, especially those under 60 years old, closure may significantly reduce the chance of another event.

The procedure involves threading a catheter through a vein in the leg up to the heart, where a small device is used to seal the opening. It’s minimally invasive, and patients usually go home the next day. Multiple large clinical trials have shown that in carefully selected patients, PFO closure can lower the risk of recurrent stroke compared to medication alone. Still, the procedure carries its own risks, including abnormal heart rhythms and rare device complications, so it isn’t appropriate for everyone.

For those who do not meet the criteria for closure or prefer a non-surgical approach, medical therapy remains standard. This may include antiplatelet drugs like aspirin or, in some cases, anticoagulants to reduce clot formation. The choice depends on the individual’s medical history, clotting risk, and physician recommendation.

Discussing PFO with Your Doctor

If you’ve had a stroke and testing revealed a PFO, the next step is a detailed discussion with your care team. Your neurologist and cardiologist will review your imaging results, consider other possible stroke causes, and evaluate whether your PFO has characteristics that make it more likely to be responsible.

It can help to ask questions such as: How large is my PFO? Did the bubble study show significant shunting? Are there any high-risk features like an atrial septal aneurysm? Would closing it meaningfully reduce my future stroke risk? And what are the potential downsides or complications?

Because each case is different, shared decision-making is essential. The final choice of what action to take often depends on your age, the pattern of your stroke, and your overall cardiovascular risk profile.

Living Well After a Stroke

Even when a PFO plays a role, overall stroke prevention involves more than closing a heart opening. Controlling blood pressure, managing cholesterol, maintaining a healthy weight, staying physically active, and avoiding smoking remain just as important. If a closure device is implanted, follow-up appointments ensure it remains well-seated and that the heart heals properly.

Recovery also extends beyond the heart. Cognitive and physical rehabilitation, emotional support, and lifestyle adjustments all contribute to better outcomes and a lower risk of recurrence.

The Bottom Line

A patent foramen ovale is common and often harmless, but in certain people it can become a hidden link to stroke. For survivors whose stroke has no clear explanation, testing for a PFO, especially through a transesophageal echocardiogram (TEE), can help determine whether it contributed to the event.

The decision to close a PFO is never one-size-fits-all. It requires thoughtful evaluation and collaboration between patient and physician. By understanding the role of PFOs in stroke and the tools used to diagnose them, survivors and families can make informed decisions about prevention and long-term recovery.