Astronauts' hearts grow rounder while they are in space, suggesting that spending lots of time in microgravity could lead to heart problems, according to US research on Saturday. That could mean trouble for people who want to embark on long-term missions to Mars.





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The astronauts' hearts returned to their normal, more oval shape, shortly after their return to Earth. Astronauts currently spend up to six months at the orbiting International Space Station, which is staffed by rotating crews. Missions to Mars, foreseen in the next couple of decades, would take about 18 months and may offer no return trip.












