The invention relates to a levorotatory enantiomer of the configurational stereoisomer of difethialone, referred to as a hetero-stereoisomer, of formula 3-(4'-bromobiphenyl-4-yl)-1-(4-hydroxythiocoumarin-3-yl)-1,2,3,4-tetrahydronaphthalene, in which the carbon atoms 1 and 3 of the 1,2,3,4-tetrahydronaphthalene group have different absolute configurations.