Our experiments using in vivo labeling techniques in the chick embryo heart have demonstrated that the straight tube heart is constituted exclusively by the primordium of the trabeculated portion of the right and left ventricles. There are, therefore, no primitive cardiac cavities. Furthermore, in the stage of looping, two new ventricular components appear, namely, the inlet and the outlet. This new information on the normal development of the heart is important in order to understand both the anatomy of the normal heart and the development of congenital malformations. Due to the fact that the straight tube heart is constituted exclusively by the primordiums of the ventricular trabeculated portions the anatomic identification of the ventricles should be made on the basis of their apical trabeculated regions. The appearance of the components of the inlet and the outlet during the process of looping is the reason for the similarity in the congenital pathology of both regions, namely, a common arterial trunk and atrioventricular septal defect with common orifice. Because the trabeculated portions of the ventricles are the oldest developmental components, they form the basis on which malformations of the inlet or the outlet, or both, are superimposed.