2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/83488In this letter we discuss how to include Breit interaction in calculations of low-energy properties of heavy atoms in accurate and effective way. In order to illustrate our approach we give some results for Cs and Tl.7 pages, LaTeX, uses IOP style, no figures. Submitted to JPBAtomic Physicstext