Benznidazole (100 mg/kg/day, p.o., 30 days) produces a decrease in electrocardiographic alterations, fewer modifications in the affinity and density of cardiac-receptors, and few isolated areas of fibrosis in the heart, in mice infected with Trypanosoma cruzi Tulahuen strain or SGO-Z12 isolate and treated at 180 days post infection (p.i.) (i.e. chronic phase) with Benznidazole.