Electrocardiographic repolarization parameters are potential markers of arrhythmogenic risk and have not been evaluated in Chagas' disease. The aim of this report was to investigate their associations with LV systolic function assessed by two-dimensional echocardiography. In a cross-sectional study involving 738 adult outpatients in the chronic phase of Chagas' disease, maximal QTc and T wave peak-to-end (TpTe) intervals, and QT, QTapex (QTa), IT and TpTe interval dispersions, and variation coefficients were measured and calculated from 12-lead standard ECGs. Clinical, radiological, ECG, and echocardiographic data were recorded. In bivariate statistical analysis, all repolarization parameters were significantly increased in patients with moderate or severe LV systolic dysfunction, and these patients showed more clinical, radiologic, and ECG abnormalities. Receiver operating characteristic curve analysis demonstrated that isolatedly QTd had the best predictive performance for LV dysfunction, with an 80% specificity and 67% sensitivity for values >60 ms in the subgroup of chagasic patients with abnormal ECGs and no heart failure. Multivariate logistic regression selected, as the best predictive model for LV dysfunction in this subgroup of patients, the presence of cardiomegaly on chest X ray (OR 14.06, 95% CI, 5.54-35.71), QTd >60 ms (OR 9.35, 95% CI, 4.01-21.81), male gender (OR 7.70, 95% CI, 2.98-19.91) and the presence of frequent premature ventricular contractions (PVCs) on ECG (OR 4.06, 95% CI, 1.65-9.97). This model showed 90% specificity and 71% sensitivity. In conclusion, QTd was associated to LV systolic function and could be used to predict asymptomatic dysfunction in chronic Chagas' disease. The presence of cardiomegaly, frequent PVCs, and male sex refined LV function stratification in these patients.