The clinical manifestations of Chagas disease are due to cell death in the target tissues that occur during the infective cycle , by sequentially inducing an inflammatory response , cellular lesions , and fibrosis . For example , intracellular amastigotes destroy the intramural neurons of the autonomic nervous system in the intestine and heart , leading to megaintestine and heart aneurysms , respectively . If left untreated , Chagas disease can be fatal , in most cases due to heart muscle damage .