A study led by a researcher at UT Southwestern Medical Center suggests that intense physical exercise during long spaceflights can help astronauts maintain the structure and function of their hearts in a way that suits the low-gravity environment of Mars. The findings, published in the journal Circulation, are important for planning future space missions and could also lead to better treatments for heart-related conditions on Earth. The study involved 14 astronauts—nine men and five women—who spent about six months aboard the International Space Station (ISS), a time frame similar to what would be needed for a journey to Mars. Before their missions, each astronaut underwent a detailed heart scan called an echocardiogram with Doppler, which uses sound waves to create images of the heart and measure its function. These scans were conducted under different simulated gravity conditions: lying flat (zero gravity), a 22% tilt (similar to Mars' gravity), and sitting upright (Earth's gravity). Once in space, the astronauts had their heart function measured again at various points during their missions—around 14, 30, 75, and 135 days, and 15 days before returning to Earth. These measurements were taken by other astronauts trained in echocardiography and Doppler techniques. Upon arrival at the ISS, the astronauts began a daily exercise routine, lasting 45 minutes to an hour, that included both endurance and strength training. In the first two weeks of their mission, all astronauts experienced some changes in their heart structure and function, with their hearts shrinking slightly. This is not unusual, as many astronauts initially experience motion sickness and are still adjusting to the demands of space life, which can limit their ability to exercise. However, over time, these changes gradually reversed, and their hearts returned closer to their original condition before the mission. After returning to Earth, the astronauts received a final heart scan under simulated zero-gravity and Mars-gravity conditions. Despite spending six months in space, their hearts showed signs of being able to function well in the low-gravity environment of Mars. The study's results may also help scientists better understand conditions like postural orthostatic tachycardia syndrome (POTS), a disorder that affects the body's ability to regulate blood pressure and heart rate when moving from sitting or lying down to standing up. This research could improve treatments for similar gravity-related health issues on Earth.