This two-part article discusses the general morphologic assessment of operatively excised cardiac valves and applies these principles to functional classifications. All cardiac valves are categorized into stenotic and purely regurgitant (no element of stenosis) groups based upon structural features: presence or absence of commissural fusion, calcific deposits, and degree and location of fibrosis. Of 2980 operatively excised cardiac valves reviewed between 1962 and 1992, the most common lesion was aortic stenosis, followed by mitral stenosis and the combination of aortic and mitral stenosis.