During a 10-year period a series of 114 patients was studied to determine if Trypanosoma cruzi and arboviruses could be the etiologic agents of idiopathic cardiomyopathy (ICM) in Cali, Colombia. In this area, ICM (together with rheumatic and atherosclerotic cardiopathy) represents the second most frequent cause (determined by necropsy) among adult patients with cardiopathies, hypertension being the first. No association was observed between ICM and any of the arboviruses assessed by hemagglutination tests. Only 10 of 114 cases (8.7%) showed positive seroparasitological tests for T. cruzi. Autopsy was performed in 4 of these 10 cases; 1 had Chagas myocarditis and the other 3 were patients with noninflammatory ICM. In all 9 T. cruzi-negative cases the autopsies showed non-inflammatory ICM lesions. In contrast to typical Chagas cases, the most frequent EKG change in ICM is left bundle branch block rather than right. Since the EKG varies within either group, this distinction may not be valid in individual cases. Because of the similarities in clinical characteristics and variations in EKG between Chagas myocarditis and ICM, it is suggested that autopsies should be done in populations in endemic areas of T. cruzi to assess the frequency of ICM and its importance in the differential diagnosis of Chagas myocarditis.