The diagnosis of complete atrioventricular septal defect (CAVSD) relies completely on echocardiography. Different measurements can be used for the differentiation of the balanced from the unbalanced forms of the defect but each of them has limitations and cannot be applied separately. There is no established algorithm ensuring precise classifi cation of the CAVSD as balanced or unbalanced, especially in borderline forms. Based on a protocol, including measurements of a series of echocardiographic parameters used by other investigators, we have managed to identify 4 measurements which when applied in a predictive model allow for correct determination of the form of the CAVSD in 97% of the cases. These parameters are: infl ow angle right ventricle/left ventricle, left atrioventricular valve infl ow, atrioventricular valve index, and ratio between the long axes of the two ventricles.