18 patients, less than one year old, with tricuspid atresia have been studied and the electrocardiographic pattern has been correlated to the hemodynamic data and type of ventriculo-arterial connection. The origin of the most frequent electro-vectorcardiographic pattern, such as the variable direction of electrical axis, left ventricular hypertrophy, the right atrial overload, the frequent counterclockwise rotation of the QRS loop on the various planes and the increased voltage of the 0.01" and LMSV spatial vectors are discussed. Moreover, the relevance of anatomic features of the two ventricles and of the position of the conduction pathways in determining the different electrocardiographic pattern in the two types of ventriculo-arterial connection, is underscored. On the basis of our results the opportunity to maintain a distinction between tricuspid atresia and single ventricle, at least from a clinical point of view, seems justified.