Normal subjects and cardiac chagasic patients without previous history of congestive failure or actual evidences of cardiac decompensation were exercised on a treadmill or a bicycle ergometer. Patients with less than the expected increase in heart rate during exercise were found to exhibit also an abnormal heart rate response to pharmacologic blockade and acute alterations in systemic vascular resistance. These results are in agreement with previous observations showing neuronal degeneration and autonomic impairment in chronic Chagas’ heart disease.