BACKGROUND The fundamental determinant of the natural history of Chagas' disease is cardiac involvement. METHODS AND RESULTS We studied 104 male patients with congestive heart failure due to Chagas' disease to estimate the survival distribution function and to evaluate age, functional class (FC), maximal oxygen consumption (VO2max), and ejection fraction (EF) as predictors of survival. Statistical evaluation was performed through univariate (Student's t test and chi 2 test) and multivariate analyses (Cox's regression model). Overall survival was 66% at 1 year, 56% at 3 years, and 48% at 5 years. Ages were not statistically different (P = .9811) between survivor (40.3 +/- 8.7) and nonsurvivor (40.3 +/- 9.4) groups. The ejection fraction(s) were statistically different (P = .0001) between survival (43.6 +/- 9.9) and nonsurvival (30.6 +/- 8.1) groups, as was VO2max (P = .0001) (21.0 +/- 4.7 and 15.0 +/- 4.9, respectively). Most of the surviving patients were in FC II and most of the nonsurvivors were in FC IV (P = .0001). VO2max (P = .0001) and EF (P = .0008) are highly associated with survival time in the multivariate analysis, but FC (P = .0578) is less important. Age (P = .9811) did not influence survival. CONCLUSIONS We conclude that 50% of the patients with heart failure due to Chagas' disease die in 47 months and that VO2max and EF are important indices of survival in this group.