The authors describe the clinical-pathologic findings in four patients with myocardial infarct (MI) associated with Chagas' disease, found among 181 autopsies of chronic congestive cardiac chagasic patients. Organized thrombo-embolus was found in the epicardial portion of a coronary artery in one instance and thrombosis in the apex of the left ventricle as well as systemic infarcts were found in all cases. These data suggest thrombo-embolism, probably from the apex of the left ventricle, as a possible cause for the regional (large; transmural) MI in chronic Chagas' heart disease. The mechanism usually operative in MI, i.e. complicated atherosclerosis, was not present in the patients of this series. Moreover, our data do not support either small artery disease or heart denervation as etiologic factors for regional MI.