A total of 70 blood-donor volunteers were studied to determine the utility of the echocardiogram and Doppler in the diagnosis of cardiopathies in asymptomatic patients with Chagas disease. These patients came from endemic areas and had humoral positive reactions for South American Trypanosomiasis. They were checked against a control group of blood-donors with no environmental antecedents and with negative reactions. Both groups were similar in age and sex. The chagasic group showed an abnormal electrocardiogram in twelve cases (17.4%), being left anterior hemiblock the most frequent alteration found (nine cases, 62.5%). In the control group no alterations were found (p = 0.0005). The echocardiogram and Doppler were abnormal in 29 cases of the chagasic group (38.8%): alterations in ventricular relaxation were found in 8 cases (27.6%), enlargement of cavities in 9 (31%), both phenomena in 9 (31%) and alteration of parietal motility in 3 (10.3%). In the control group, 1 case presented alteration in ventricular relaxation (p = 0.000008). These results confirmed that the abnormal discoveries were related to Chagas disease. Out of 70 chagasic patients, 31 (44.29%) showed some alteration in the tests: 12 had an abnormal electrocardiogram, and of these only 2 had normal echocardiogram and Doppler, the rest showed abnormal echocardiogram and Doppler. Other 29 (of these 70 patients) showed some alteration in the echocardiogram and Doppler, and 20 of them presented a normal electrocardiogram. It can be concluded that the echocardiogram and Doppler are more accurate to detect cardiac involvement in asymptomatic chagasic patients than the electrocardiogram, showing abnormality in many cases where there are no electrocardiographic alterations. On the other hand, patients with abnormal electrocardiogram and Doppler are less frequent. Therefore, to define the undetermined period of Chagas disease echocardiogram and Doppler should be incorporated as a routine resource of diagnosis considering the high percentage of cases in which cardiac participation is detected when there is no clinic, radiologic and electrocardiographic disturbance.