The authors studied the pathological features of 106 hearts of patients with Chagas' heart disease who died suddenly. These patients had not had symptoms in any phase of their Hves. The macro and microscopic studies demonstrated that under the qualitative point of view, the lesions are similar to those observed in hearts of patients who died with heart failure. On the other hand the intensity of the lesions observed in the hearts of the chagasic patients with sudden death is of lesser degree than of those who died in heart failure. Based upon the obtained data, the possible mechanisms of sudden death are discussed. The authors conclude that neither the involvment of intrinsec nervous system of the heart, the degree of inflammatory lesions nor the presence of parasites in the myocardium can be related to the sudden death. The findings that couid elucidate the problem are probably related with certain pathological aspects such as: lesion of conducting tissue of the heart, regressive lesions of myocardial fibers and disorders of the immune system.