Dilated and contracted forms of primary endocardial fibroelastosis: a single fetal disease with two stages of development. Left ventricular endocardial fibroelastosis was diagnosed by echocardiographic scanning in a fetus at 20 weeks' gestation. Repeated prenatal examination over the next 20 weeks' gestation showed the development of the left ventricle from a chamber with a dilated cavity to a small cavity with a very thick wall. These findings were confirmed at necropsy and by the absence of other morphological anomalies. The contracted form of primary fibroelastosis in the fetus must have followed an insult that prevented any further increase in the size of the left ventricular cavity. 