The heavy quarks - charm and bottom, constitutes a unique probe of the Quark Gluon Plasma (QGP) properties. The basic concepts related to the study of the dynamics of the heavy quarks in the quark-gluon plasma created in heavy-ion collisions at relativistic energies will be discussed. I shall discuss the difficulties of the present theoretical approach to provide a self-consistent description of the experimental data both at BNL-RHIC and CERN-LHC. The importance of the temperature dependence of the drag coefficient on the "heavy quark puzzle" will be discussed. In the second part of my presentation the assumption of Brownian motion for the charm quarks will be challenged. The results on the dynamical evolution of charm and bottom quarks obtained within the ambit of Fokker-Planck approach will be compared with the results from Boltzmann transport equation. I will show that while for bottom the motion appears quite close to a Brownian one, this does note seems to be the case for charms quarks. In particular the solution of the Boltzmann equation gives larger anisotropic flow than the flow obtained in Fokker-Planck approach. This improves the description of experimental data or takes us closer to the solution of the "heavy quark puzzle". Finally I shall highlight the impact of pre-equilibrium phase, hadronic phase as well as the effects of transient electro-magnetic field on the heavy quark dynamics.