**3. Pathogenesis**

This is a multisystem condition, of unknown etiology, which affects the lungs in most patients (90%) and usually involves the nodes and mediastinum. Cardiac involvement varies according to the population studied and can reach up to 25% [3]. The typical histological feature is the presence of non-necrotizing granuloma (see **Figure 1**) [6] with a central area rich in macrophages, epithelial cells, giant multinucleated cells, and T CD4-positive lymphocytes. In the periphery, there is an abundant population of T CD8 and CD4 lymphocytes, mast cells, and fibroblasts [7]. The origin of this condition is unknown, but one of the theories proposed is antigenic stimulation due to occupational and environmental exposure and infectious agents such as mycobacteria [8].

#### **Figure 1.**

*Cardiac tissue biopsy. Fragments of myocardium can be observed with compromise due to multiple epithelial, non-necrotizing, focal, and coalesced granules, which involve about 30% of the tissue analyzed. The granules contain numerous multinucleated giant cells and, in the confluent areas, are associated with interstitial fibrosis. Stains were negative for mycobacteria and fungi.*
