Trypanosomes can take on a number of morphological forms during their life cycle. These forms are distinguished by the characteristics of the flagellum and kinetoplast. The particular forms vary from species to species. In Trypanosoma cruzi one stage is the amastigote, which is found in cells of the heart of various species of mammal, including humans. The amastigote is small and spheroidal, and the flagellum has degenerated to the point that it does not extend beyond the pellicle. The amastigote multiplies in the muscles of the heart by binary fission, destroying the heart tissue. Some amastigotes transform into trypomastigotes and enter the circulatory system. These circulating trypomastigotes do not multiply, but may re-enter heart tissue or be picked up by a blood-feeding insect vector.
This photo shows a small accumulation of amastigotes within a cyst in cardiac muscle. The nucleus is visible in many, and the short internal flagellum can be seen in a few.