Chagas' disease is a public health problem in Venezuela, affecting people living in rural areas. 30% of the patients evolve to a Chronic Chagasic Myocardiopathy (CCM) characterized by heart failure, arrhythmias, incapacity to work and sudden death. There are not predictive factors to determine the evolution from the indeterminate form of the disease (asymptomatic form) to CCM. In the present paper we have studied 115 patients enrolled in the Cardiology unit at the Baudilio Lara Hospital in Quibor (Lara State, Venezuela) and 12 healthy patients coming from the same area. Patients were evaluated by means of clinical history; echocardiography, electrocardiography and radiology. The presence of anti-T. cruzi antibodies and levels of Tumor Necrosis Factor alpha (TNFalpha) were determined in serum samples. Chagas' disease patients were classified in 3 groups: I (asymptomatic), II (asymptomatic with normal left ventricular ejection fraction (LVEF) and electrocardiographic alterations) and and III (symptomatic, electrocardiographic alterations and LVEF < 70%). The results showed that 33.04% of the patients had anti-T. cruzi antibodies in their serum; we also observed a significant increase in the serum levels of TNFalpha in groups I and III of Chagas' disease patients as compared with the control healthy group. Chagas' disease patients belonging to Group II displayed similar TNFalpha levels as controls. We observed a statistically significant (p < 0.05) negative correlation between serum TNFalpha values and LVEF. Patients suffering of non-chagasic myocardiopathy had a significant increase of TNFalpha as compared with control patients and similar levels to those observed in Chagas' disease group III patients. These results confirm that the elevation of TNFalpha serum levels could be a immunopathogenic mechanism in the evolution of myocardiopathies.