In your blood of course. Specially if you inject it, then it takes even longer to get out of your system. If you inject every day and it's about two wax paper bags or more then I would say 4-8 days in blood. If it's in the urine then 1 day[if you only used once] to 5 days if your a chronic user. Heroin is water soluble so if drink a lot of water it will come out a lot faster.