Background: Left atrial (LA) and left ventricular (LV) diastolic function analysis can yield new strategies to recognize early cardiac involvement and prognostic indicators in Chagas disease. Methods: Patients with Chagas disease with the indeterminate (n= 69) or with the cardiac form (32 with changes limited to electrocardiography [stage A], 25 with changes in LV systolic function but no heart failure [HF; stage B], and 26 with HF) underwent evaluation of LV diastolic function (mitral inflow, pulmonary vein flow,color M-mode echocardiography, and tissue Doppler analysis), and LA function by three-dimensional echocardiography and strain analysis and were prospectively followed for the occurrence of clinical events. Echocardiograms were also obtained from 32 controls. Results: LV diastolic dysfunction was gradually more prevalent and severe across groups from patients with the indeterminate form of Chagas disease to patients with HF. Tissue Doppler was the best tool to demonstrate the worsening of LV diastolic function across the groups (E' velocity: controls, 12.662.3 cm/sec;patients with the indeterminate form, 12.163.1 cm/sec; stage A, 10.362.9 cm/sec; stage B, 8.362.8 cm/sec; patients with HF, 5.661.9;P< .0001). Although maximum LA volume was increased only in pa-tients with HF, minimum LA volume (controls, 862 mL/m2; patients with the indeterminate form, 862 mL/m2; stage A, 963 mL/m2; stage B, 1164 mL/m2; patients with HF, 27617 mL/m2;P< .0001) and precontraction LA volume (controls, 1163 mL/m2; patients with the indeterminate form, 1263 mL/m2; stage A, 1364 mL/m2; stage B, 1665 mL/m2; patients with HF, 32619 mL/m2;P< .0001) were increased in all cardiacform groups. LA conductive function was depressed in all cardiac form groups, while LA contractile functionwas depressed only in patients with HF. Cox proportional-hazards regression analysis revealed that end-systolic LV diameter (hazard ratio, 1.6; 95% confidence interval, 0.9–2.8;P= .09), E' velocity (hazard ratio,0.5; 95% confidence interval, 0.3–0.8;P= .001), and peak negative global LA strain (hazard ratio, 1.21;95% confidence interval, 1.02–1.4;P= .03), were independent predictors of clinical events.Conclusions:LV diastolic dysfunction was found in all forms of chronic Chagas disease, including those without LV systolic dysfunction. LV diastolic dysfunction may contribute to changes in LA volume and conductive function found in early stages of the cardiac form. Both LV diastolic function and LA contractile function were independent predictors of clinical events.