20 patients with endocardial cushion defects were studied. Partial forms of common atrioventricular canal and those associated with complex congenital malformations were not considered. The right and left ventricular inflow and outflow tracts were measured and average values of inflow tract/outflow tract were calculated for each anatomical form of the disease. We found this ratio to be significantly smaller in Group B2 compared to Group B1 of Enriquez de Salamanca's classification, the first group being considered to be a more severe congenital malformation than the second. The inflow tract/outflow tract ratio of the right ventricle ranged between 80% and 50%, with an average of 62.3% in Group B1 compared to 62% and 24% with an average of 49% in Group B2. Using Studert's test, this difference was shown to be statistically significant (p = 0.02). On the other hand, there was no correlation between the other parameters or between the severity of the anatomical lesions and the clinical condition. The reduction of the right ventricular inflow tract may give an indication as to the type of atrioventricular valve which may be present.