Endocardial fibroelastosis was first reported by Kreysig, in 1816, under the misnomer of fetal endocarditis.1 New concepts have developed in the understanding of this condition, especially since 1941. This term is now generally accepted as embracing various entities, including adult forms. Andersen and Kelly,2 in 1956, showed that many children with congenital heart disease develop endocardial fibroelastosis, apparently secondary to hemodynamic factors or anoxia in the malformed heart. A single group remains unassociated with other cardiac abnormalities, and this is termed "primary" endocardial fibroelastosis.3 The etiology of primary endocardial fibroelastosis is not certain, but it has been suggested that this lesion is a genetically determined developmental anomaly, possibly due to an enzymatic defect of the myocardium.1 The occurrence of primary endocardial fibroelastosis in siblings is rare. An accumulation of data on such familial cases might support the theory of a familial metabolic disorder, as well as