A familial study was undertaken on 382 probands with transposition of the great vessels, 348 with coarctation of the aorta and 143 with hypoplastic left heart syndrome. It allowed to assess in sibs the frequency of identical congenital heart diseases (respectively 0.15, 0.42 and 3.41%) and of all 7.32%). The epidemiological study did not provide further data worth noting. At the origin of the transposition of the great vessels, tetratogenetic factors are added to genetic factors, whose part is of little importance; hypoplastic left heart syndromes are heterogeneous (recessive autosomal transmission, chromosome abnormalities, sporadic cases). Coarctations of the aorta, which are dependent on different mechanisms are also heterogeneous. It is possible that common factors, whether hereditary or not, play a part on one hand in hypoplastic left heart syndromes and coarctations of the aorta, and, on the other hand, in some congenital heart diseases.