“…However, we know no report about the use of the max:min RR ratio for detecting vagal dysfunction in Chagas' disease on an outpatient care basis. The active orthostatic stress test is sensitive, specific, reproducible, and easily performed, being con- Table I The results of the active orthostatic stress test in chagasic patients with no heart disease, as compared with that in normal controls, confirm the findings of our previous study performed in the same group of patients [4][5][6] , and in another sample later studied 7,8 , and also the findings reported by other authors [24][25][26][27] . The different methods used, such as the variability in heart rate (assessed with different techniques) 5,7,8,22 , the Valsalva maneuver 6,23,24,26 , and respiratory sinus arrhythmia 5,26 , showed that autonomic dysfunction is present in patients with no evidence of heart disease and with preserved left ventricular function.…”