Exact analytical solution for the space-time evolution of electromagnetic field in electrically conducting nuclear matter produced in heavy-ion collisions is discussed. It is argued that the parameter that controls the strength of the matter effect on the field evolution is σγb, where σ is electrical conductivity, γ is the Lorentz boost-factor, and b is the characteristic transverse size of the matter. When this parameter is of the order 1 or larger, which is the case at the Relativistic Heavy Ion Collider and the Large Hadron Collider, the space-time dependence of the electromagnetic field completely differs from that in vacuum.