  Heavy flavor hadrons have long been considered as a probe of the quark gluon
plasma created in high energy nuclear collisions. In this paper we review the
heavy flavor properties under extreme conditions and the realization in heavy
ion experiments. After a short introduction on heavy flavor properties in
vacuum, we emphasize the cold and hot nuclear matter effects on heavy flavors,
including shadowing effect, Cronin effect and nuclear absorption for the former
and Debye screening and regeneration for the latter. Then we discuss, in the
frame of transport and coalescence models, these medium induced changes in open
and closed heavy flavors in nuclear collisions and the comparison with
nucleon-nucleon collisions. Considering the extremely strong electromagnetic
and rotational fields generated in non-central nuclear collisions, which are
widely studied in recent years, we finally investigate their effects on heavy
flavor production and evolution in high energy nuclear collisions.
