Abstract: This paper discusses significant effect of particular structure of biomolecular ligands and electronic structure of metal cation on the basic toxicity mechanism of heavy metals at the molecular level, which is supported on the examples such as an antagonism between Pb(II) and Ca(II) on the physiological activity, an influence of replacement metals on Zinc enzyme activity, an inordinately strong affinity of Hg(II) and Pb(II) toward thiohydroxy (-SH) resulted from toxicity.