Genetic and environmental factors are the two areas which have received attention in the etiology of congenital cardiac malformation. Genetic factor in many types of congenital heart disease have not been clearly delineated. Congenital heart diseases are a heterogenous category of developmental anomalies, representing in most cases the multifactorial inheritance of threshold characters, the expression of which is the product of a genetic - environmental interaction. Recently we experienced three pairs of congenital heart disease in siblings including ventricular septal defects in twin.[KTCS 1981;1:87-90]