  A study of heavy flavor production in different collision systems in various kinematic regions presents an opportunity to probe cold nuclear medium and hot dense matter effects. Results from the PHENIX experiment on $J/\psi$ and open charm production in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ =200 GeV are presented. The data show strong $J/\psi$ suppression in central AA collisions, similar to NA50 results, and strong suppression in high $p_T$ open charm production. The $J/\psi$ production in Au+Au and d+Au collisions is compared to understand the cold nuclear medium effects. The data show significant cold nuclear effects in charm production in d+Au collisions at forward and backward rapidity ranges. 
Heavy Flavor Production at PHENIX at RHIC