  We calculate the transverse momentum dependence of the medium-induced gluon
energy distribution radiated off massive quarks in spatially extended QCD
matter. In the absence of a medium, the distribution shows a characteristic
mass-dependent depletion of the gluon radiation for angles smaller than m/E,
the so-called dead cone effect. Medium-modifications of this spectrum are
calculated as a function of quark mass, initial quark energy, in-medium
pathlength and density. Generically, medium-induced gluon radiation is found to
fill the dead cone, but it is reduced at large gluon energies compared to the
radiation off light quarks. We quantify the resulting mass-dependence for
momentum-averaged quantities (gluon energy distribution and average parton
energy loss), compare it to simple approximation schemes and discuss its
observable consequences for nucleus-nucleus collisions at RHIC and LHC. In
particular, our analysis does not favor the complete disappearance of energy
loss effects from leading open charm spectra at RHIC.
