How does microgravity affect us, in paricular our cardiovascualar system and heart functioning?
One well known effect is that under microgravity, bones start to weaken.
The effects of microgravity on human physiology is one of the things being studied on the International Space Station. I'd have to check around to see what the latest data area, but as Monique said, there is a loss of bone mass (very serious concern). Also, muscles weaken from lack of use (something which can be fixed).
How does microgravity affect functioning of our heart?
Based on Phobos' reply, I would assume that the muscles in the heart would also become weakened due to the reduced effort required to pump blood around the body.. so a returning pilot may have difficulties once back on earth.
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