The morphology of 50 normal tricuspid valves was studied. The surface of the leaflets was divided into three zones: (1) the rough zone, into which most of the chordae tendineae are inserted, (2) the basal zone, and (3) the clear zone, which lies between the rough and basal zones.Five types of chordae were distinguished by their morphology and mode of insertion: fan-shaped, rough zone, basal, free edge, and deep chordae. The last two types are unique to the tricuspid valve.If fan-shaped chordae, used to define the commissures between the leaflets, are absent, other landmarks may be used for commissural definition. Once defined, all tissue between the commissures was regarded as part of the anterior, posterior, or septal leaflet. The recognition that the free edges of the anterior and septal leaflets contain notches, that rough zone chordae insert into them, and that the posterior leaflet has scallops further aids identification of a leaflet's components. Thus, structures formerly regarded as accessory leaflets were incorporated into one of the three leaflets.RECENTLY, we have reexamined the morphology of the mitral valve and have been able to establish a better clinicopathologic correlation in various types of mitral valve abnormality. By identifying the specific fan-shaped chordae tendineae attached to the mitral valve, we were able to delineate the commissural areas clearly and to divide the valve into anterior and posterior leaflets. We were, thus, also able to identify the clefts of the posterior leaflet and to distinguish them from the true commissures.1 2 This definition of mitral valve anatomy eliminates the need to postulate accessory leaflets of the mitral valve. It proved valuable in enhancing clinicopathologic understanding of the syndrome of mitral regurgitation due to prolapse of the posterior leaflet.3

Fifty normal mitral valves from adults were studied. Commissures, identified by commissural chordae tendineae and the tips of papillary muscles, partition the mitral valvular tissue into anterior and posterior leaflets. This definition incorporates into the posterior leaflet the structures formerly regarded as accessory leaflets. The posterior leaflet is further divided into scallops by clefts in its tissue. Cleft chordae provide a guide to these interscallop indentations or clefts. Partitioned this way, the posterior leaflet was tri-scalloped in 46 hearts. In 42, a large middle scallop was present with two smaller scallops on either side. Rough and clear zones can be defined on the anterior leaflet and rough, clear, and basal zones on the posterior leaflet. Additional Indexing Words: Commissure Prolapsed mitral valve Chordae tendineae Mitral regurgitation

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