Patent Foramen Ovale and Decompression Illness

By Rubicon Foundation editorial team

5 min read · 1 November 2026

A patent foramen ovale (PFO) is a flap-like opening between the heart’s upper chambers that may remain after birth. In diving medicine, the question is whether this route can let venous gas bubbles enter arterial circulation and contribute to decompression illness—an issue with implications for diagnosis, risk assessment and dive planning.

What does a PFO change in circulation?

After birth, the opening between the right and left atria usually closes, but in some people it remains capable of opening under particular pressure conditions. A PFO is not the same as a continuously open hole: blood flow across it can be intermittent and depends on the pressure difference between the two atria.

Venous gas bubbles can form during decompression and are commonly filtered by the lungs. If a right-to-left shunt allows bubbles to bypass that filter, they may reach the arterial circulation. This is called paradoxical embolism; it offers a plausible pathway linking a cardiac shunt with some decompression-related neurological or other manifestations.

How can bubbles and decompression illness be linked?

Decompression illness covers decompression sickness and arterial gas embolism. These conditions have different mechanisms, although symptoms can overlap and clinical distinction may not be straightforward. A PFO is most relevant to the proposed passage of venous bubbles into arterial blood; its presence alone does not establish that a particular illness was caused by a shunt.

Bubble formation and illness are not interchangeable. Divers can have circulating venous bubbles without symptoms, while decompression illness can occur without a known PFO. The relationship is therefore a question of interacting factors: bubble production, the shunt’s anatomy and function, dive exposure, and the clinical presentation.

What do studies in this area examine?

Research brings together cardiac testing, decompression physiology and clinical observation. Investigators may assess whether a shunt is present and whether it can pass blood from right to left, then consider that information alongside a diver’s symptoms and exposure history. Different tests and protocols can identify different aspects of shunt function, so methods matter when comparing findings.

Studies also distinguish association from causation. A PFO may be more relevant in a particular clinical pattern or exposure context than in another, but a finding on a heart test does not by itself explain an episode. The broader research task is to understand when the proposed mechanism has practical significance and how confidently it can be identified.

Shunt anatomy and function: whether a route between the atria exists and permits right-to-left passage.
Decompression exposure: the dive profile and conditions that shape inert-gas uptake and elimination.
Clinical presentation: the timing and nature of symptoms, interpreted in a medical assessment.
Study design: how testing, case definitions and comparison groups affect what can be inferred.

Why does the question matter to divers and clinicians?

For divers, the issue is not simply whether a PFO is present, but whether it changes the interpretation of decompression risk in an individual case. For diving physicians and hyperbaric clinicians, the possible shunt is one element in assessing decompression illness, alongside the dive history, symptoms and other potential explanations.

Testing and decisions about diving carry their own practical consequences. Screening is not a substitute for diagnosing symptoms, and a positive result needs clinical interpretation. Anyone with suspected decompression illness needs urgent assessment; questions about PFO testing or return to diving should be discussed with a physician experienced in diving medicine.

How does this fit into decompression research?

Decompression research has long examined how inert gas moves into and out of tissues, how bubbles form, and why exposures with similar profiles can have different outcomes. The PFO question adds a cardiovascular route to that picture: it asks whether a pathway that bypasses pulmonary filtration helps explain a subset of illness, rather than replacing established work on decompression and bubble dynamics.

The subject sits at the intersection of cardiology and diving medicine. Its practical value depends on connecting a physiological mechanism to clinical patterns without treating a risk factor as a diagnosis. The key next question for any diver is how a specialist interprets the person’s symptoms, exposure and cardiac findings together.

Frequently asked questions

Does having a PFO mean a diver will develop decompression illness?

No. A PFO is a possible route for venous bubbles to enter arterial circulation, not a diagnosis or a guarantee of illness. Its significance depends on the clinical and diving context.

Can decompression illness occur without a PFO?

Yes. Decompression illness has multiple mechanisms, and a PFO is only one proposed factor in some cases. The absence of a known shunt does not rule out decompression illness.

Should divers seek PFO screening?

Screening decisions depend on the individual circumstances and the potential consequences of testing. A physician experienced in diving medicine can discuss whether assessment is appropriate and how any result would affect care or diving decisions.

An original research-library explainer written by the Rubicon editors. It is not a summary of a specific publication.