What is the tolerance of heroin?

It all depends on the person; whether their tolerance for opiates is low, high, or non-existent. Judging by the fact that you are asking this question, I would guess that you have no tolerance to opiates, so the smallest amount possible should be used (preferably none). Tolerance is built by repeatedly consuming opiates (heroin, hydrocodone, oxycodone, meperidine, morphine, etc) for a period of time. Eventually your tolerance will increase and it will require more and more of the same chemical to reach the desired effect.