The author studied the electrocardiograms of four adult dogs suffering from Chagas' Disease in the chronic stage. These electrocardiograms were made before and after the dogs had been injected intravenously with the antigen of Schizotrypanum cruzi prepared by using cultures of this flagellate in Bonacci's medium. The quantity of trypanosomes injected varied from 0.12 to 3.8 millions per kilo. The electrocardiographic tracings made at varying intervals up to 48 hours after the injection of the antigen showed no significant alteration.