How Long Could You Live Without A Heart?

It depends... If your supported by cardiac pump you'll live for it can
replace the function of heart. But if you don't, I think you'll die within
3-10 minutes but your cells/tissues die as far as I can recall its about
2 days.

Okay say a man donates his heart to save a life how does the donor than live if they take his heart out?

You can not live without your heart. Your heart is an extremely important part of the human body and without it, you are dead. Under certain circumstances, a person may be placed on a machine temporarily that does that job of the heart until a new donor organ is found.