In line with this, Zhang and coworkers suggested that the embryonic epicardium and derived mesenchymal cells were the major source of fibroblasts in endocardial fibroelastosis (EFE), a pathological condition characterized by diffuse profound thickening of the endocardium with abnormal deposition of collagen and elastin predominantly in the left ventricle, often associated with hypoplastic left heart syndrome (HLHS) [160]. The gene discussed is ELN; the disease is endocardial fibroelastosis.