That's one of the conclusions from a recent health study of 12 astronauts, the results of which were presented at this past weekend's American College of Cardiology’s 63rd Annual Scientific Session.
The study is part of NASA's larger effort to better understand the health risks associated with extended periods of time spent under zero-gravity conditions.
"The heart doesn’t work as hard in space, which can cause a loss of muscle mass," explained study leader Dr. James Thomas, who serves as the Moore Chair of Cardiovascular Imaging and Lead Scientist for Ultrasound at NASA. "That can have serious consequences after the return to Earth, so we’re looking into whether there are measures that can be taken to prevent or counteract that loss."
Extended space travel can also result in diminished bone density and muscle mass, as well as vision anomalies.
The 12 astronauts participating in the study provided heart shape measurements -- among other health tests -- before, during and after their space missions. As NASA doctors had predicted, the results showed average astronaut heart become rounder by a factor of 9.4 percent.
Scientists say further research needs to be conducted to understand how this shift in heart shape might affect function.
Astronauts already have a number of special exercises they do to keep their hearts healthy while floating about up in the cosmos, but this new research could help them perfect those routines and prevent heart problems for astronauts returning to Earth.