  A fully relativistic calculation of the double photoionization of helium-like
atoms is presented. The approach is based on the partial-wave representation of
the Dirac continuum states and accounts for the retardation in the
electron-electron interaction as well as the higher-order multipoles of the
absorbed photon. The electron-electron interaction is taken into account to the
leading order of perturbation theory. The relativistic effects are shown to
become prominent already for the medium-Z ions, changing the shape and the
asymptotic behaviour of the photon energy dependence of the ratio of the
double-to-single photoionization cross section.
