AbstractOn the basis of both developmental and morphological evidence, we would suggest that a ventricle is best defined as any chamber within the ventricular mass possessing an apical trabecular component. Such ventricles can be of right or left morphology, and always coexist. The ventricles are normally formed when possessing all three of the inlet, apical trabecular, and outlet components, but incomplete when lacking one or both of the inlet and outlet components. Ventricles that are incomplete because of lack of the inlet component are always hypoplastic, with incomplete right ventricles being positioned antero-superiorly within the ventricular mass, and incomplete left ventricles located postero-inferiorly. Patients having such incomplete ventricles because of the lack of the inlet component have functionally univentricular hearts, although the functionally univentricular arrangement can also be produced in the setting of normally constituted but hypertrophied ventricles. Full analysis of ventricular morphology, therefore, requires attention not only to component make-up, but also size.