The possibility of "back to the past"

Well, the most heated way is that build a machine that can accelerate so rapidly that the speed or velocity can exceed the speed of light...

When there's a machine that can go faster than light, then we can possibly go back to the past of future by the relativity, but then it's not feasible for human body, coz the heart cannot withstand the high pressure generated by the high speed. So, lots of problems arises =[