Straddling and Displaced Atrioventricular Orifices and Valves

Among the unusual forms of congenital cardiac disease are (1) the entities of single ventricle and (2) the rare situation in which the tricuspid valve (communicating with the right atrium) joins either the left ventricle alone ("displaced tricuspid valve") or both ventricles ("straddling tricuspid valve"). The subjects of displaced or straddling tricuspid valve occupy the main body of a report by Dr. Liberthson and associates (Circulation 43:213, 1971). According to the author, while single ventricle and the other two conditions are quite different entities from an anatomic viewpoint, they are closely related developmentally, an opinion which I wish to emphasize. The relationship is supported by a consideration of the highlights of the development of the ventricles of the fourchambered heart. In the primitive heart, the common atrium is joined to the common ventricle by the common atrioventricular canal. Normally, the latter gives rise to the mitral and tricuspid valves. Development of two ventricles depends upon a focus of growth in the wall of the primitive ventricle, from which the right ventricle is molded, while the tissue intervening between the