[The atrio-ventricular junction: descriptive aspects].

An attempt is made to give a new, revised and more adapted description of the atrio-ventricular junction. This description is based on our personal observations and on data collected from the anatomical and embryological literature of the last 30 years. A fibrous layer interrupting muscle continuity exists between the atria and the ventricles. This non conductive fibrous structure - classically referred to as an Atrio-Ventricular Ring - is not a tendinous ring (LOWER) or a cordlike annulus: it is a fragile lamina which also serves as anchorage for the A-V valves. In no way, can it provide a secure site for the placement of sutures in valve surgery. Both on mitral and tricuspid sides, the so-called A-V ring has a crescentic shape rather than an oval or circular shape. It is best divided into two segments for descriptive purposes: an aorto-septal and a scissural segment: The aorto-septal segment (antero-medial) is thicker and tougher. It presents close, important and dangerous relation-ships - with the postero-lateral part of the aortic root, - and with the vital structures located in the complex junctional zone of the 4 heart cavities (carrefour des cavites cardiaques). The scissural segment (postero-lateral) which forms the deepest part of the A-V fissure, is represented, on both sides, by the subvalvular lamina. This horseshoe shaped lamina is thin and fragile. It is easily stretched following the A-V ostium enlargement, resulting in functional mitral or tricuspid insufficiency.