Arterioventricular relations and their classification. Two specimens of arterioventricular discordance and review of published reports.

We present a theory which makes it possible to interpret the relation between the different types of truncoconal morphologies and the position of the ventricles, to establish the atrioventricular relations, and to integrate them in the context of the corresponding visceral situs. This theory is based onfindings from experimental embryology, i.e. that the cardiac tube is constituted by three segments with specific features which appear at different de- velopmental stages and which give rise to three different heart regions (the atria, the ventricles, and the great arteries with their valvular planes) and on the evidence that the heart is formed by two cardiac primordia with different developmental potentialities.