The main theoretical aspects of the heavy-flavour production at ultra-high
cosmic ray energies are reviewed, with particular emphasis in the new
dynamical effects which are expected to be present in the kinematical
range probed by the IceCube and Pierre Auger Observatories. The gluon
saturation effects for heavy quark production and the contribution of
double parton scattering processes are analysed. Finally, the
intrinsic heavy quark hypothesis is presented and some of its
phenomenological implications at high energies are discussed.