Astronauts’ Hearts Reveal an Unexpected Ability That Could Help Future Mars Missions

After nearly six months in space, 13 astronauts helped scientists examine how the human heart adjusts to prolonged weightlessness and responds when gravity returns.

Researchers from Northwestern University, UT Southwestern Medical Center, and other institutions found that certain measures of heart function initially declined, then recovered toward earlier levels.

The astronauts also showed no greater cardiovascular stress under simulated Martian gravity than they had experienced standing upright before their missions. Published in the American Heart Association journal Circulation, the findings offer evidence relevant to the planning of future human missions to Mars.

The study was first published online on September 15, 2026, and appeared in the journal’s October 13 issue. It addresses a concern that spacecraft technology alone cannot resolve: how astronauts’ bodies will function after months in space beyond Earth’s gravity.

The researchers concluded that difficulty tolerating Martian gravity is unlikely after about six months of spaceflight, provided existing physical countermeasures are maintained.

How Scientists Simulated Martian Gravity to Test Astronauts’ Hearts

The experiment examined how the cardiovascular system responds as gravity pulls blood back toward the lower body. Researchers wanted to understand whether astronauts returning from months of weightlessness could withstand the gravitational conditions they would encounter on Mars.

Mars has approximately 38% of Earth’s gravity. To simulate part of that gravitational effect, researchers placed the returning astronauts at a 22-degree upward tilt from a lying position.

The results addressed a key concern for future exploration: whether astronauts might struggle to maintain normal circulation after months in weightlessness.

Dr. Benjamin Levine of UT Southwestern discussed the outcome in a September 15 interview with STAT.

“That was really reassuring to me,” he said.

The researchers’ conclusion was more cautious than declaring astronauts ready for Mars. The evidence suggests that difficulty tolerating upright posture under Martian gravity may be unlikely under the conditions examined.

How Astronauts’ Heart Function Changed During Six Months in Space

The researchers observed early reductions in cardiac filling and blood pumped per beat, followed by recovery toward preflight measurements. These findings showed that the heart changed measurably during prolonged exposure to weightlessness, but those changes did not remain constant throughout the missions.

The study included nine men and four women, with an average age of 49. Their median mission duration aboard the International Space Station was 164 days.

Scientists used echocardiograms, ultrasound scans that reveal the heart’s structure and pumping activity, to monitor the astronauts before, during, and after their missions.

Crew members performed the examinations on one another and transmitted the images to specialists on Earth. Dr. James Thomas, a Northwestern University cardiologist and senior author of the study, sometimes guided the scans remotely.

During the first two weeks, researchers detected reductions in cardiac filling and stroke volume. These measurements describe how much blood enters the heart before contraction and how much blood is ejected with each beat.

Over subsequent months, the measurements approached their preflight supine values, meaning the levels recorded while the astronauts were lying down.

The pattern gave researchers a more complete picture of how cardiovascular function changes throughout prolonged exposure to weightlessness. The original study in Circulation details the findings.

Related: 7 Ways Alcohol Hurts Your Heart And Ages You Fast

Why Daily Exercise May Have Helped Astronauts Maintain Heart Function

The cardiovascular changes were observed in astronauts who followed established physical training routines throughout their missions. Researchers examined heart function under conditions where regular exercise was already part of astronauts’ daily schedules.

According to a Northwestern University research summary, the astronauts exercised up to two hours daily, combining endurance and resistance training.

“You lose muscle mass and cardiac mass when you’re in a weightless environment because you are working less up there,” Thomas explained. “To counter that, exercise is crucial when you’re in space,” he added.

The study excluded astronauts who avoided exercise, so researchers couldn’t isolate the precise contribution of physical training to the results.

That distinction also leaves unanswered how the cardiovascular system might respond if an astronaut couldn’t maintain the exercise program.

Why Earth-Based Tests Cannot Fully Recreate a Mars Landing

The astronauts underwent testing after returning to Earth, where they had immediate access to medical assistance. While these examinations offered valuable information about cardiovascular responses to simulated Martian gravity, the testing environment differed considerably from an actual landing on another planet.

In his interview with STAT, Levine acknowledged that returning crew members received substantial medical support and that some were given intravenous fluids.

Comparable assistance might be harder to provide during an actual Mars landing.

The experiment also reproduced only certain cardiovascular effects of Martian gravity. It did not recreate every physical demand of arriving and working on another planet.

These limitations matter because the study involved just 13 astronauts and missions lasting about six months, not the full duration of a round-trip to Mars.

What the Findings Mean for Future Mars Missions

The research provides detailed evidence of cardiovascular adaptation that scientists can use when preparing for human exploration beyond Earth. By examining how heart function changed during prolonged weightlessness and under simulated Martian gravity, the study offers a clearer picture of the challenges future crews may encounter.

By monitoring astronauts throughout their missions, researchers could observe changes that pre-launch and post-landing examinations might have missed.

The findings help define what existing exercise countermeasures may accomplish, while identifying conditions that future investigations will need to examine.

The larger challenge remains unchanged. Building a spacecraft capable of reaching Mars is one engineering task; ensuring that its crew can function after the journey is another.

For now, the study adds a carefully measured piece of evidence to that effort.

Will the cardiovascular responses observed under controlled conditions also hold during an actual journey to another planet?

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