Characterized by an increased amount of connective tissue and elastic fibers causing a thickening in the muscular lining of the heart, endocardial fibroelastosis (EFE) is a rare condition eventually leading to congestive heart failure if it is not diagnosed early. Whereas some studies advocate that EFE may be the result of an X-linked, autosomal recessive trait, others support that EFE is caused by intrauterine viral infections, impaired lymphatic drainage of the heart, or carnitine deficiency.