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Astronauts' hearts on the ISS: a dip, adaptation, and a simulated Mars-gravity test
The full story behind my Short: A Circulation study of 13 astronauts on ~6-month ISS missions found heart filling and stroke volume dipped in the first two weeks, then recovered towards pre-launch levels; after landing, a 22° head-up tilt simulating Mars gravity showed no major strain.
The short version
Could the human heart cope with a trip to Mars? A study in Circulation followed the hearts of 13 astronauts through about six months on the International Space Station, using ultrasound (echocardiogram) scans they performed on each other every few weeks. In the first two weeks, cardiac filling and stroke volume (blood pumped per beat) fell, but then they gradually improved, approaching pre-launch levels. The astronauts exercised up to two hours a day (30–45 minutes of endurance and 60–75 minutes of resistance training), which likely helped. Mars has about 38% of Earth's gravity, so a 100 kg astronaut would feel about 38 kg there. After landing, each astronaut was tilted 22 degrees head-up from lying down to mimic Mars gravity's effect on blood flow, and their hearts performed just as well as when standing upright on Earth before the mission. Caveat: just 13 people and a simulation, not Mars (Appadurai et al., Circulation, 2026; Northwestern Medicine, UT Southwestern, UTHealth Houston).
13astronauts, about six months each on the ISS [1]
2 weeksearly dip in cardiac filling and stroke volume, then recovery towards pre-launch levels [1]
22°head-up tilt after landing to simulate Mars gravity's effect on the blood [1]
~38%Mars surface gravity compared with Earth's [1]
What they found
Researchers from Northwestern Medicine, UT Southwestern and UTHealth Houston (senior author Dr. James Thomas, with Dr. Benjamin Levine and Dr. Michael Bungo) collected echocardiograms (heart ultrasound scans) before, during and after missions of about six months on the International Space Station. Astronauts were trained to scan one another every few weeks, and the recordings were sent to Earth; Thomas often watched live, at about 3 a.m. his time, coaching them to improve the images [1].
During the first two weeks in space, cardiac filling (how much blood enters the heart between beats), stroke volume (how much it pumps out per beat) and several other measures declined. As the missions went on, filling and stroke volume gradually improved, approaching pre-launch levels. The astronauts followed NASA's exercise countermeasures, up to two hours a day: 30 to 45 minutes of endurance training and 60 to 75 minutes of resistance training [1].
To mimic Mars, which has roughly 38% of Earth's surface gravity, each astronaut was tilted 22 degrees upward from lying down after returning to Earth, shifting blood towards the lower body as Martian gravity would. After about six months in space, their hearts performed just as well under this simulated Martian gravity as they had when standing upright on Earth before their missions, with no significant signs of cardiovascular strain [1]. The study is described as the first to test the heart under simulated Martian gravity after a long spaceflight [1].
Watch the Short
About this page
The “100 kg astronaut would feel about 38 kg” comparison is my own arithmetic from Mars's ~38% gravity. The tilt-table photo in the Short shows ESA's Alexander Gerst on a tilt table during pre-launch tests in 2014 (NASA photo), used as an illustration, not a photo from this study. The heart-curve sketch shows the direction of the changes only, not data values. NASA images are public domain (credited below).
The narration is an AI clone of my own voice (Chatterbox), used with my consent.
Why it matters
- Mars planning. It is encouraging evidence that astronauts could travel to Mars and work on the surface without major cardiovascular problems [1].
- Exercise matters. Daily endurance and resistance exercise likely helped keep their hearts in shape [1].
- Small and simulated. Only 13 astronauts, and a tilt table is not a Mars landing, so more research is needed [1][2].
Full narration (transcript)
Could your heart survive a trip to Mars? Thirteen astronauts just gave us a surprising answer. A new study in Circulation followed their hearts through about six months on the space station. In weightlessness, the heart barely fights gravity, so it can shrink. Every few weeks, they scanned each other's hearts with ultrasound. At first, their hearts pumped less blood per beat. Then they adapted, back towards pre-launch levels. What probably helped: up to two hours of exercise every day. And here's where it gets interesting: Mars has about 38 percent of Earth's gravity. A 100-kilo astronaut would feel just 38 kilos. So back on Earth, they tilted each astronaut up 22 degrees from lying down, to mimic Mars gravity on the blood. Their hearts did just as well as standing upright on Earth before the mission. One caveat: that's just thirteen people, and a tilt table isn't Mars. Why it matters: it's a hopeful sign that astronauts could reach Mars, and actually work there. For the full story, follow the link in the description.
Sources
- [1] Northwestern University (2026). “Astronauts’ hearts just passed a surprising test for Mars.” ScienceDaily, 21 October 2026. sciencedaily.com
- [2] Appadurai, V., Negishi, K., Borowski, A.G., Popović, Z.B., Greenberg, N.L., Martin, D.S., Bungo, M.W., Levine, B.D. & Thomas, J.D. (2026). “Impact of Prolonged Spaceflight on Cardiac Structure and Function: An Exploratory Longitudinal Observational Study.” Circulation 154(15): 1444. DOI 10.1161/CIRCULATIONAHA.125.078665. doi.org
Credits
Images: NASA, public domain, via Wikimedia Commons: Possible exploration of the surface of Mars.jpg (NASA/Pat Rawlings, Public domain); Good Morning From the International Space Station.jpg (NASA/Scott Kelly, Public domain); ISS-30 Dan Burbank uses the Integrated Cardiovascular Resting Echo Scan.jpg (NASA, Public domain); ISS-36 Cassidy on T2 in Node 3 module.jpg (NASA, Public domain); Mars globe.jpg (NASA/USGS, Public domain); Tilt table Gerst.jpg (NASA/Victor Zelentsov, Public domain); This illustration of Moon to Mars infrastructure shows astronauts living and working on the surface of Mars (Moon to Mars Infrastructure).png (NASA, Public domain). Sketches and animation: my own. Narration: AI clone of Nasper Mushonga's own voice (Chatterbox TTS by Resemble AI, MIT licence), used with his consent.