科学美国人60秒:Absence (of Weight) Makes the Heart Grow Rounder

When astronauts float weightless in space, their muscles don't need to work as hard as on Earth. Muscles therefore atrophy during a long mission, which can cause trouble when space travelers return home. But what happens to that most vital of muscles, the heart?
 
To find out, 12 astronauts learned how to do ultrasound scans of their hearts. Then they recorded the organ's shape before, during and after a stint on the International Space Station. The scans showed that while in microgravity the astronauts' hearts deformed into more spherical shapes. Back on Earth, they stretched back into their usual elongated forms. The work was presented at the annual scientific session of the American College of Cardiology. [Chris May et al, Affect of Microgravity on Cardiac Shape: Comparison of Pre- and In-Flight Data to Mathematical Modeling]

Knowing how weightlessness changes the heart could help mission planners prevent long-term damage to astronauts’ cardiovascular systems due to long space voyages. Astronauts on the space station already perform specific exercises to keep their weight-bearing muscles toned. Similarly well-designed workouts might keep hearts both in shape—and in the right shape.

—Sophie Bushwick