Normally and abnormally related great arteries: what have we learned?

The conus arteriosus or infundibulum was the site of the major cardiovascular evolutionary and developmental adaptation that made possible air-breathing and permanent land-living for vertebrates, including mammals such as ourselves. The subarterial conal free walls perform an embryonic aortic switch procedure by 35 to 44 days of age in utero, based on growth of the left-sided subpulmonary conal free wall and resorption of the right-sided subaortic conal free wall, i.e., complete right-left asymmetry in the development of the subarterial conal free walls. There is only one way of doing the developmental aortic aortic switch procedure right (one way in situs solitus, and its mirror-image in situs inversus), and there are many ways of doing it wrong, resulting in the conotruncal anomalies. The proximal or apical part of the conus arteriosus, the septal band, was the mother of the right ventricular sinus (the lung pump). The conus transformed the single (systemic) circulation of fish into our double (systemic and pulmonary) circulations. The right ventricle (RV) is only about 36% as old as the left ventricle (LV). Most congenital heart disease involves anomalies of the more recently developed RV, congenital heart disease being the most frequent anomaly in liveborn children - almost 1 percent (0.8%).