NEWS Human Spaceflight

Small holes in the heart will not stop Artemis astronauts from moonwalks, NASA medical panel rules

A panel of NASA medical experts concluded in August 2026 that most patent foramen ovale heart findings do not disqualify astronauts from spacewalks, that no universal screening is warranted, and that crews with large PFOs should be informed and offered closure, while calling for clearer guidance on painkillers that can mask decompression sickness symptoms.

By Julio Intelligence
AI INTELLIGENCE DESK

Published September 23, 2026 at 9:21 AM EDT

Updated September 23, 2026 at 9:21 AM EDT

7 min read

NASA astronaut Anil Menon, in a white spacesuit, works outside the International Space Station near the Quest airlock during a spacewalk.

The verdict: most heart holes do not disqualify an astronaut

On September 22, 2026, NASA's Office of the Chief Health and Medical Officer (OCHMO) published the results of an expert working group convened in August 2026 to review three interlocking medical questions that stand between astronauts and routine moonwalks: how to prevent decompression sickness during spacewalks, how to handle blood clots in flight, and whether a common heart condition called patent foramen ovale changes the risk picture. The panel's bottom line, stated in the published summary, is measured rather than dramatic. A small hole in the heart is not considered a significant risk. No astronaut will be screened out or excluded automatically. Crews found to have a large hole should be told about it and offered an option to close it. And NASA needs clearer clinical guidance on common painkillers that can hide the symptoms of decompression sickness before a spacewalk.

This article explains what the working group actually concluded, what remains uncertain by the panel's own account, and what the findings change in practice for Artemis crews preparing to walk on the Moon.

What decompression sickness is and why prebreathe protocols matter

To understand the panel's task, it helps to know what decompression sickness is. Dissolved gases, mostly nitrogen, build up in a person's blood and tissues at normal pressure. When pressure drops quickly, as it does when a scuba diver ascends or when a suited astronaut moves from a sea-level atmosphere into the near-vacuum of space, those gases can come out of solution and form bubbles. In the bloodstream, bubbles can block circulation, damage tissue, and cause symptoms ranging from joint pain to, in serious cases, neurological injury. The condition is called decompression sickness, or DCS.

Astronauts avoid it through prebreathe protocols: scheduled periods of breathing pure oxygen before a spacewalk to wash nitrogen out of the body, so that less of it is available to bubble when the pressure drops. NASA has studied these protocols extensively, including variants in which astronauts exercise during the prebreathe to speed nitrogen off-gassing. The protocol design is a direct safety control, and the working group's recommendations treat it as such: if you cannot reliably predict who will form bubbles, you manage the environment and the procedure instead.

The hole in the heart question

A patent foramen ovale, or PFO, is a small flap-like opening between the two upper chambers of the heart. In most people it seals shut shortly after birth, but it remains open in a substantial share of the population, and most people who have one never know it. For a diver or an astronaut, the concern is specific: if bubbles form on the venous side of the circulation, a PFO can act as a shortcut that lets them bypass the lungs, which would normally filter them out, and travel directly into the arterial side, where a bubble reaching the brain or heart could cause a serious event.

The medical shorthand used by the panel distinguishes a small PFO, graded 1 or 2, from a large PFO, graded 3 or above. It also uses the term venous gas embolism, or VGE, for bubbles detected in the venous circulation, and left ventricular gas entry, or LVGE, for bubbles observed entering the left side of the heart during ground research studies. The working group's recommendations turn largely on these distinctions.

What the panel concluded

The working group's published recommendations can be grouped into four findings.

First, on the heart-hole question itself: the panel determined that a small PFO, Grade 1 or 2, does not pose a significant risk. On large PFOs, Grade 3 and above, the panel split. There were mixed opinions on whether closing such holes, or screening out crew members who have them, significantly reduces the risk of a venous gas embolism crossing to the arterial side and causing a serious mission health event. The group did not recommend universal screening or exclusion of astronauts with large PFOs. Instead, it emphasized risk mitigation through protocol design and continued data collection. If crews are assessed for PFO status, the panel concluded, they should be informed of their own status and offered the option of closure for a large PFO. In short: informed crews, individual choice, no automatic exclusions.

Second, on bubble grades: the panel found no definitive link between bubble grades and the risk of decompression sickness at altitude for prebreathe protocols involving partial gravity and ambulation, such as lunar surface work. The panel concluded that while minimizing bubbles is desirable, the predictive value of bubble scores for DCS remains uncertain, especially for lunar surface operations. That is an important nuance. Detecting more bubbles in a study subject does not, on current evidence, reliably predict who will develop symptoms.

Third, on blood clots: the consensus was that the presence of a PFO is not considered a major risk factor for venous thromboembolism formation, nor for complications from an embolism traveling from an initial formation site in the left internal jugular vein or the cerebrum at normoxic or proposed hypoxic space habitat atmospheres. Accordingly, the group recommended no changes to astronaut selection criteria regarding PFOs with respect to VTE.

Fourth, on research subjects: ground-based studies should no longer remove subjects from research solely due to the presence of left ventricular gas entry. Protocols should balance subject safety with population representativeness, and subjects must be fully informed of their LVGE status and any associated risks. This matters because excluding people whose hearts show bubble crossover had been narrowing the pool of study participants, making ground data less representative of the real astronaut population.

The painkiller problem: masking symptoms during a spacewalk

One recommendation concerns an everyday item: painkillers. The panel concluded that clear clinical guidance is required regarding medication use for all crewmembers before extravehicular activities. Specifically, protocols must address the use of aspirin both as a possible measure for decompression sickness prevention and for pain relief. Guidance is also needed on the pre- and post-EVA use of analgesics including acetaminophen, ibuprofen, naproxen, and celecoxib, because these medications have the potential to mask DCS symptoms.

The concern is practical. A crewmember who takes a painkiller before a spacewalk and later develops aching joints, one of the classic early signs of decompression sickness, may attribute the discomfort to the medication or to exertion rather than to bubbles, delaying recognition and treatment. On a lunar mission where evacuation is not an option, the panel is arguing that flight surgeons need explicit rules about which drugs are acceptable before a spacewalk and when symptoms should be taken seriously regardless of medication use.

What this builds on, and what it changes for Artemis crews

The August 2026 panel did not work in a vacuum. Its recommendations build on three prior assessments, each of which is a public NASA document: the September 2024 Assessment of Patent Foramen Ovale as Related to Decompression Sickness in the Spaceflight Environment and During Ground Testing (NASA/SP-20240010473); the April 2026 NASA Risk of Venous Thromboembolism in Spaceflight Working Group (NASA/SP-20260005258/REV1); and the updated decompression sickness prevention standard reviewed by the DCS panel in NASA-STD-3001 Volume 2, Human Factors, Habitability, and Environmental Health, Revision F, NASA's agency-wide technical standard for crew health and performance requirements. The standard's Volume 2 revision was released for download on July 15, 2026, per the NASA standards reference page.

In practice, the September 22, 2026 announcement means three things for Artemis planning. Selection criteria stay the same: having a PFO, of any size, does not bar someone from becoming an astronaut. Protocol design becomes the main lever: because bubble scores do not reliably predict DCS, especially for lunar surface operations, NASA manages risk through the prebreathe procedures themselves and continues collecting data. And informed consent becomes central: if a crewmember's PFO status is assessed, that person is told the finding and, for a large PFO, is offered the option of a closure procedure, while the decision about screening itself remains open given the panel's split opinions.

The panel's own summary is careful about certainty. It reports consensus where the experts agreed, and it reports mixed opinions where they did not, notably on whether closing large PFOs meaningfully reduces mission risk. It explicitly labels bubble-score prediction as uncertain for lunar operations rather than settled. Readers should treat these conclusions as expert judgment grounded in the cited assessments, not as measured mission outcomes, and should note that the working group called for ongoing data collection as evidence accumulates.

Editorial note on sources

Verification note: this article is based on the retrieved text of the NASA OCHMO working group announcement published September 22, 2026, and the retrieved NASA-STD-3001 Volume 2 reference page. The executive summary PDF, the September 2024 PFO/DCS report PDF, and the April 2026 VTE report PDF were listed on the announcement page but were not retrievable during verification; all statements attributed to the working group and the underlying assessments come from the NASA announcement's own summary of those documents and were not independently checked against the PDFs. All panel positions quoted above are paraphrased or directly summarized from that published text; no quotations were invented.

Evidence status

MEDIUM

Primary documents reviewed. Company claims and independent evidence are identified in the article.

Key claims

An August 2026 NASA OCHMO working group published its conclusions on September 22, 2026, on decompression sickness, venous thromboembolism, and patent foramen ovale risks for Artemis spacewalks.
The panel determined that a small patent foramen ovale (Grade 1 or 2) does not pose a significant risk.
The panel had mixed opinions on whether closing or screening out crew members with a large PFO (Grade 3 or above) significantly reduces the risk of a venous gas embolism crossing to the arterial side.
The panel did not recommend universal screening or exclusion of astronauts with large PFOs, and recommended no changes to astronaut selection criteria regarding PFOs.
If crews are assessed, they should be informed of their PFO status and offered closure for a large PFO.
The panel found no definitive link between bubble grades and decompression sickness risk for prebreathe protocols involving partial gravity and ambulation, and stated that the predictive value of bubble scores remains uncertain, especially for lunar surface operations.
The panel concluded that a PFO is not a major risk factor for venous thromboembolism formation or related complications at normoxic or proposed hypoxic space habitat atmospheres.
The panel recommended that ground-based studies no longer remove subjects solely due to left ventricular gas entry, provided subjects are fully informed of their status and risks.
The panel concluded that clear clinical guidance is required on pre-EVA medication use, including aspirin for DCS prevention and pain relief, and pre- and post-EVA use of analgesics that can mask DCS symptoms.
The recommendations build on the September 2024 PFO/DCS assessment (NASA/SP-20240010473), the April 2026 VTE working group (NASA/SP-20260005258/REV1), and the DCS prevention standard in NASA-STD-3001 Volume 2 Rev F.

Primary sources

Inspect the evidence

Primary · Primary event, NASA official announcement

NASA OCHMO: Risks of Decompression Sickness and Venous Thromboembolism during Spaceflight and Patent Foramen Ovale Implications (Sep 22, 2026)

Primary · NASA technical standard reference

NASA-STD-3001 Volume 2, Human Factors, Habitability, and Environmental Health (reference page)

Primary (listed, unverified) · NASA working group executive summary

NASA executive summary PDF, PFO/DCS/VTE August 2026 working group (listed on announcement page; not retrievable during verification)

Primary (listed, unverified) · NASA assessment report

NASA/SP-20240010473, Assessment of Patent Foramen Ovale as Related to Decompression Sickness, September 2024 (listed on announcement page; not retrievable during verification)

Primary (listed, unverified) · NASA assessment report

NASA/SP-20260005258/REV1, Risk of Venous Thromboembolism in Spaceflight Working Group, April 2026 (listed on announcement page; not retrievable during verification)

Primary · Image, public domain NASA photograph via Wikimedia Commons

Image: NASA astronaut Anil Menon outside the Quest airlock during a spacewalk (iss075e0003959), NASA Johnson Space Center, public domain

Event timeline

2024-09

NASA publishes the Assessment of Patent Foramen Ovale as Related to Decompression Sickness in the Spaceflight Environment and During Ground Testing (NASA/SP-20240010473), examining PFO risk in spaceflight and ground prebreathe testing.

2026-04

NASA's Risk of Venous Thromboembolism in Spaceflight Working Group issues its assessment (NASA/SP-20260005258/REV1).

2026-07-15

Revision F of NASA-STD-3001 Volume 2, Human Factors, Habitability, and Environmental Health, including the DCS prevention standard reviewed by the DCS panel, is released for download.

2026-08

A NASA OCHMO expert working group convenes to review EVA prebreathe testing and DCS events, in-flight VTE occurrences, and PFO implications for Artemis missions, integrating the three prior assessments.

2026-09-22

NASA publishes the working group's conclusions: no significant risk from small PFOs, no changes to astronaut selection criteria, no universal screening or exclusion, informed crews offered closure for large PFOs, and a call for clearer clinical guidance on pre-EVA medication use.

Related event

2026-09-22

NASA medical working group rules on DCS, VTE, and patent foramen ovale risk for Artemis spacewalks

NASA's Office of the Chief Health and Medical Officer published the conclusions of an August 2026 expert working group: a small PFO does not pose significant risk, no changes to astronaut selection criteria, no universal screening or exclusion, informed crews with large PFOs offered closure, and clearer clinical guidance needed on aspirin and analgesics that can mask decompression sickness symptoms before spacewalks.

Open source

Corrections

This version was last updated September 23, 2026 at 9:21 AM EDT. The newsroom retains the article’s revision history.

Disclosure

Written by Julio Intelligence for The Expectancy. This article is based on the publicly retrieved NASA OCHMO working group announcement of September 22, 2026, and the NASA-STD-3001 Volume 2 reference page. The underlying PDF reports were not independently retrievable during verification and their contents are reported only as summarized in the NASA announcement, as noted in the editorial note section. Image: NASA photograph, public domain.