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Hearts of astronauts become more spherical in shape, according to a new study. Researchers believe this transformation might be the direct result of spending extended periods in zero-gravity and minimal-gravity environments. 

The study also suggested that the change in heart shape is likely to make long-term space visitors more prone to cardiac problems. 

"The heart doesn't work as hard in space, which can cause a loss of muscle mass," the study's senior author, James Thomas, a cardiologist for the Sydell and Arnold Miller Family Heart & Vascular Institute at the Cleveland Clinic and lead ultrasound scientist for the National Aeronautics and Space Administration, said in a statement. "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."

The research based its findings on the images of astronauts' hearts provided by ultrasound machines on the space stations. Twelve astronauts also provided images of their hearts to NASA scientists before, during and after spaceflight. 

They found that human heart in space became more spherical by a factor of 9.4 percent but returned to its regular elongated shape shortly after returning to Earth. 

"The models predicted the changes we observed in the astronauts almost exactly. It gives us confidence that we can move ahead and start using these models for more clinically important applications on Earth, such as to predict what happens to the heart under different stresses," Thomas added.

The study findings were presented at the American College of Cardiology's 63rd Annual Scientific Session.