Enlargement of the membranous ventricular septum: an internal stigma of Down's syndrome.

A study of heart specimens without ventricular septal defect from patients with down's syndrome showed a significant enlargement of the membranous ventricular septum as compared to the normal heart. This increase in area of the ventricular septum occupied by membranous tissue from 2 to 9% may not only predispose patients with Down's syndrome to congenital heart disease, but may be one end of a spectrum of cardiac anomalies related to malalignment or maldevelopment of the ventricular septum in Down's syndrome.