This three-part article examines the histologic and morphologic basis for stenotic and purely regurgitant tricuspid valves. In Part III, morphometric analysis of tricuspid valve annular circumference, leaflet area, and the product of annular circumference and leaflet area are shown to be useful in establishing etiology for the purely regurgitant tricuspid valves and in assessing the anatomic basis of pure tricuspid regurgitation in the presence of mitral stenosis.