Is it dangerous for you whole arm to be badly bruised after blood test while on heparin after pulmonary embolism?

They should not have drawn blood on the arm to which you had a hepain going for this simple reason. Heparin is a blood thinner, which prevents proper clotting of blood; in combination with a puncture from blood draw you would get quite a blue arm, but no worries, as long as that is all that there is it will go away in a weeks's time.