CLEVELAND -

One could argue astronauts have braver hearts than most. They may have rounder hearts too.

New research finds that an astronaut’s heart actually changes shape in outer space due to the lack of gravity. Cleveland Clinic cardiologist Dr. James Thomas led the study. He says on Earth, gravity pulls the heart into the pericardium, the sack around the heart, and gives the heart an oblong shape. But that’s not the case in space.

“When we’re standing up, the heart hangs down and the pericardium exhibits a little bit of constriction on the heart," said Thomas. "When we go into space, it basically floats away and the pericardium has no effect and the heart just naturally becomes a little more globular up in space.”

Thomas and a team of NASA researchers studied 12 astronauts who worked on the International Space Station for an average of 6 months. Their hearts were tested before, during and after spaceflight using a heart ultrasound machine.

Results show that the astronauts’ hearts became more spherical by 9.4 percent, meaning it was a little wider and shorter, up in space.

They also found that once an astronaut returns to Earth, the heart goes back to its normal shape almost immediately.

The study is part of a larger trial to determine why some astronauts pass out upon returning from space. The heart’s changing shape may play a role.

“When they return to Earth however, there is the risk of several abnormalities, the most worrisome of which is orthostatic hypotension. That’s a fancy phrase for when they stand up their blood pressure drops low and they may pass out," said Thomas.

The astronauts, who had only received a few hours of ultrasound training, were able to successfully image their own hearts in space. Thomas says using ultrasound in an extreme environment like space can be translated to care in other remote areas here on Earth.

“This is a model that we are now extending to our work bringing ultrasound to the field in Africa, in India, in South East Asia," said Thomas. "It’s such an inexpensive technology that it might have great benefit for developing areas of the world.“

In preparation for a potential trip to Mars, Thomas’ team also conducted tests to see how the heart would respond on a long mission to the red planet, which has one-third the gravity of earth.