Objective-To analyse the morphological aspects of the extracellular matrix and microcirculation to clarify whether chronic Chagas' cardiopathy (CCC) is an accurate model to study the pathogenesis of idiopathic dilated cardiomyopathy (IDCM). Design-Thick histological myocardial sections were prepared to analyse collagen, and microcirculation was examined during confocal laser and light microscopy. Setting-The specimens were prepared at the pathology service of the Heart Institute of Sã o Paulo, Brazil. Patients-Nine control hearts, eight IDCM hearts, and 10 CCC hearts were studied after necropsy. Main outcome measures-The number of collagen struts per 100× field, the area of fibrosis (%), and the diameters of arterioles and capillaries were measured in each heart to establish outcome. Results-A smaller number (mean (SD)) of collagen struts was seen in the hearts in the IDCM group (9.1 (4.1)) than in the control (22.4 (3.2)) (p < 0.05) or CCC (15.7 (7.4)) (p > 0.05) groups. Fibrosis was greater in the CCC hearts (13.8 (10.5)%) than in the IDCM hearts (5.9 (6.6)%) (p > 0.05). Major increases in arteriole (65.4 (9.9) µm) and capillary (9.9 (1.7) µm) diameters were seen in the CCC hearts but not in the IDCM hearts (arteriole diameter 40.3 (7.9) µm; capillary diameter 7.9 (1.3) µm). Conclusions-Hearts demonstrating CCC and IDCM present diVerent extracellular and microvessel alterations. This suggests that distinct pathogenic mechanisms are responsible for each condition and that CCC is not an eVective model to study IDCM. (Heart 1999;82:279-285)

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