Immune homeostasis has been suggested to play an important role in the clinical evolution of chronic Chagas disease; however, the immunopathologic factors involved have not been fully elucidated. Therefore, our study aimed to analyse the frequency of CD4+ CD25+ FoxP3+ cells, classic Th17 cells, alternative Th17 cells and IL-17+ B cells from peripheral blood of chronic cardiac patients after in vitro stimulation with Trypanosoma cruzi soluble EPI antigen. Patients were selected and classified according to clinical evaluation of cardiac involvement: mild, B1 (CARD1) (n = 20) and severe, C (CARD2) (n = 11). Patients with the indeterminate form of CD were included as the control group A (IND) (n = 17). Blood samples were collected and cultured in the presence of EPI antigen. Cells frequency and median fluorescence intensity (MFI) were obtained by flow cytometry. Our results showed that only CD4+ CD25+ FoxP3+ , CD4+ CD25high FoxP3+ , CD4+ IL-17+ IFN-γ- and CD4+ IL-17+ IFN-γ+ cells are more frequent in patients with severe cardiac disease and correlate with worse global cardiac function. However, while indeterminate patients demonstrated a positive correlation between CD4+ CD25+ FoxP3+ and CD4+ IL-17+ IFN-γ- Th17 cells, this relationship was not observed in cardiac patients. IL-17 expression by Th17 cells and B cells correlated with disease progression. Altogether our results suggest that the clinical progression of Chagas cardiomyopathy involves worsening of inflammation and impairment of immunoregulatory mechanisms.2050-01-01