Endocardial fibroelastosis (EFE) is a congenital heart disease which is characterized by thickening of the inner lining of the left ventricle, thickening and malformation of the cardiac valves, and hypertrophy of the heart. Put in another words, endocardial fibroelastosis is the diffuse patchy thickening of the mural endocardium, particularly in the left ventricle, due to proliferation of collagenous and elastic tissue; often associated with congenital cardiac malformations. It appears as unexplained heart failure in infants and children. Endocardial Fibroelastosis is a rare heart disorder usually associated with children two years old and younger. It is an uncommon cause of unexplained heart failure in infants and children, and is one component of HEC syndrome.
The term "endocardial fibroelastosis" was introduced by Weinberg and Himmelfarb in 1943. In their pathology laboratory they noted that usually the endocardium was pearly white or opaque instead of normally thin and transparent and microscopically showed a systematic layering of collagenous and elastic fibers. they felt their new term was more adequately descriptive, and, indeed it was quickly and widely adopted. Clinicians began applying it to any infant with a dilated, failing heart, in spite of the fact that the only way to definitively establish the presence of EFE was to see it at autopsy. EFE had quickly become the name of a disease, and it continues to be used by many physicians in this way, though many patients with identical symptoms do not have the endocardial reaction of EFE.