RECENT pediatric and pathologic literature has reported a larger number of cases of fetal endocardial fibroelastosis than during any previous era.1We have studied one of these cases, the features of which were so unique and of such extreme degree that we thought it timely to add our case to the literature. This condition, described in the latter half of the 19th century, is characterized by a non-inflammatory fibrosis of the mural and valvular endocardium, particularly in the left cardiac chambers. Usually both aortic and mitral valves are involved, and often the myocardium is hypertrophied. Occasionally the right side of the heart dilates and hypertrophies, and congenital defects are often found, such as aortic hypoplasia, transposition of the great vessels, patent ductus arteriosus (Botalli), and patent foramen ovale. Although true inflammatory changes are lacking, the condition has been called fetal endocarditis. The endocardium is thickened by an increase in