A panel of outside physicians and NASA specialists has advised the agency against universally screening or excluding astronauts who have a patent foramen ovale, a small opening between the heart's upper chambers, as NASA prepares for Artemis missions to the Moon and beyond. The recommendations were posted on September 22, 2026, by NASA's Office of the Chief Health and Medical Officer, which convened the working group in August.

The panel concluded that a small patent foramen ovale, or PFO, does not pose a significant risk. Members held mixed opinions on whether closing or screening out a large PFO would meaningfully reduce the chance of a gas bubble crossing into the arteries and causing a serious health event during a mission. In the end, the group "did not recommend universal screening or exclusion of astronauts with large PFOs."

These are recommendations to NASA, not a formal change to astronaut selection rules. They matter because the question bears directly on how NASA plans to protect crews during lunar surface work, and because the condition is common in the general population.

A Common Condition in a Harsh Environment

Before birth, everyone has a small opening in the wall between the heart's upper chambers, and it usually closes on its own after birth. When it stays open, doctors call it a patent foramen ovale. "About 1 in 4 people has one, and most never know it," according to the American Heart Association.

For most people, a PFO causes no problems. The spaceflight concern involves decompression sickness, the condition divers call the bends. When astronauts move into a lower-pressure spacesuit, nitrogen dissolved in the body can form bubbles in the blood. The lungs normally filter those bubbles out, but a PFO could, in theory, let some bypass the lungs and travel to the brain or other organs.

NASA reduces that risk with prebreathe protocols, in which crews breathe oxygen before a spacewalk to flush nitrogen from their bodies. Lunar surface operations add new variables, including partial gravity and walking in a suit, and the panel said the evidence for those conditions remains limited.

Inside the Panel's Recommendations

According to the working group's executive summary, the panel reached six main recommendations.

On blood clots, the consensus was that a PFO is not a major risk factor for forming a clot in space or for complications if one travels. Clots seen in spaceflight have historically formed in the left internal jugular vein in the neck and in the cerebral sinuses, and none have occurred in the legs. The panel noted that blood returning from the upper body is directed away from the wall where a PFO sits. It recommended no changes to astronaut selection criteria regarding PFOs with respect to clot risk.

On decompression sickness, the panel noted that diving studies show a large PFO raises the risk of the bends about fivefold, but that the absolute risk in diving remains extremely low when established safe procedures are followed. No definitive studies have examined the link between PFO and decompression sickness at altitude, and the panel said conservative prebreathe protocols may protect people with small PFOs.

The group found no definitive link between bubble counts measured by ultrasound and decompression sickness risk for protocols involving partial gravity and walking, and said the predictive value of bubble scores remains uncertain for lunar surface operations. It advised that ground studies stop removing volunteers solely because bubbles appear on the left side of the heart, so that study groups better represent real crews. If crew members are assessed, the panel said, they should be told their PFO status and offered closure for a large one.

The panel also called for clear guidance on medications before and after spacewalks. NASA currently gives aspirin before spacewalks to reduce decompression risk, but the panel said that practice rests mainly on limited animal studies rather than human trials. It warned that combining aspirin with apixaban, a clot-prevention drug, significantly increases bleeding risk, and that common pain relievers can mask decompression symptoms. For suit-related pain, it suggested acetaminophen as the first option.

Evidence Gaps the Panel Flagged

The working group was an expert review, not a new clinical trial. It built on NASA's earlier assessment of PFO and decompression sickness from September 2024, an April 2026 review of blood clot risk in spaceflight, and the decompression sickness standard in the agency's human spaceflight health standard, NASA-STD-3001.

The panel was candid about uncertainty. It said translating diving data to altitude is difficult because no definitive trials exist, that bubble scores have uncertain predictive value for lunar operations, and that its members were divided on large PFOs. It also called for current decompression sickness treatment protocols to be formally tested.

Invited panel members included cardiologists, hematologists, specialists in hyperbaric and diving medicine, a neurologist, and retired NASA astronaut Mike Gernhardt. Representatives of the Canadian, European, and Japanese space agencies also attended.

What It Means Beyond Spaceflight

The findings concern spaceflight and do not change medical guidance for the public. The panel noted that current clinical guidelines do not recommend routine PFO closure unless a patient has had a stroke with no other identified cause or recurrent neurological decompression sickness.

That context may interest people who scuba dive. Recreational divers who know they have a PFO, or who have had unexplained decompression symptoms, should discuss their situation with a physician familiar with diving medicine. According to the American Heart Association, most people with a PFO need no treatment.

The panel also reviewed studies of people living at altitudes below 8,000 feet, the range NASA is considering for future habitats, and found no clinically significant increase in blood clot rates compared with sea level. The report does not address commercial air travel.

NASA's Decision Still Ahead

NASA's posting presents the working group's recommendations; it does not announce changes to astronaut selection rules or give a timeline for any. The review was framed around Artemis missions to the Moon and beyond.

The largest open question is how bodies respond to partial gravity and walking during long lunar surface activities. The panel's emphasis on protocol design and ongoing data collection suggests that evidence will build gradually from ground tests and future missions.

If NASA follows its advisers, a common heart variation would not, on its own, keep an otherwise qualified astronaut off the Moon. For everyone else, the report is a reminder that a PFO is usually harmless and that questions about it belong with a doctor.

What Readers Want to Know

What did the NASA panel recommend?

It advised against universal screening or exclusion of astronauts with a patent foramen ovale, found that small PFOs pose no significant risk, and called for clearer medication guidance around spacewalks.

Is this a new NASA policy?

No. These are recommendations from a working group convened by NASA's Office of the Chief Health and Medical Officer. The posting does not announce changes to astronaut selection rules.

What is a patent foramen ovale?

It is a small opening between the heart's upper chambers that stays open after birth. About one in four people have one, and most never know it.

Why does a PFO matter in space?

During spacewalks, nitrogen bubbles can form in the blood. A PFO could let some bubbles bypass the lungs, which is why NASA studies it in relation to decompression sickness.

Should divers with a PFO be concerned?

Diving studies link large PFOs to a higher risk of decompression sickness, though the absolute risk stays very low with safe practices. Divers with concerns should consult a physician familiar with diving medicine.

Does this affect ordinary air travel?

No. The report addresses spacewalks and space habitats, not commercial flights.

What happens next?

NASA will decide whether and how to use the recommendations for Artemis missions. No timeline has been announced.