Hello Ameen

Your question is an interesting one, but because people who enter space remain in an earthlike atmosphere while on the shuttle or in the station there is very little available data on the exact physical reaction of the human heart entering space. With that being said, NASA has conducted experiments with the objective of understanding the human bodies ability to perform with out the influence of gravity. Im not sure if this will help, but the experiment number for an in space cardiovascular test performed in 2004 was 99-03-046/99-03-377

You might also check this book out,

http://books.nap.edu/openbook.php?record_id=10614&page=80

I hope this was helpful