An analysis of the intracardiac autonomic nervous system (ICANS) has been made in 150 histological sections obtained from atrial fragments of a 74 year-old man who died of cardiac failure, as a consequence of acute Chagas' disease (ACD), probably acquired via digestive tract. Small quantities of mononuclear infiltrate around ganglia and/or nerve branches without significant morphologic alterations of the neurons were found in 10 slides; another slide showed ganglionitis and periganglionitis of moderate intensity associated to neuronal alterations. Focal epicarditis, usually of slight degree, was observed in all slides. The findings suggest: a) that the inflammation of ganglia and fibers of the ICANS in the ACD occurs at least in part by expansion from adjacent epicarditis; b) that even in the fatal cases of the trypanosomiasis cruzi the pathologic lesions of the ICANS may be slight.