  We present the first study of the quark mass dependence of the heavy quark
momentum and spatial diffusion coefficients using lattice QCD with light
dynamical quarks corresponding to a pion mass of 320 MeV. We find that, for the
temperature range 195 MeV $<T<$ 293 MeV, the spatial diffusion coefficients of
the charm and bottom quarks are smaller than those obtained in phenomenological
models that describe the $p_T$ spectra and elliptic flow of open heavy flavor
hadrons.
