Valvular involvement by disease causes stenosis, insufficiency (regurgitation), or both. Stenosis is the failure of a volve to open completely, thereby impeding forward flow Insufficiency, regurgitation, or incompetence, in contrast results from failure of a valve to close completely, thereby allowing reversed flow. These abnormalities can be either pure, when only stenosis or regurgitation is present or mixed when both stenosis and regurgitation coexist in the same valve, but one of these defects usually predominates. Dysfunction may affect a single valve (isolated disease) or multiple valves (combined disease). Functional regurgation results when a valve becomes incompetent owing to ventricular dilation, which causes the right or left ventricular papillary muscles to be pulled down and outward thereby preventing coaptation of otherwise intact leaflets during systole. Abnormalities of flow often produce abnormal heart sounds known as murmurs.

Valvular dysfunction can vary in degree from slight and physiologically unimportant to severe and rapidly fatal. The clinical consequences depend on the valve involved the rate and quality of compensatory mechanisms. For example, sudden destruction of an aortic valve cusp by infection (as in infective endocarditis) may cause rapidly fatal caardiac failure owing to massive regurgitation. In contrast, rheumatic mitral stenosis usually develops over years and its clinical effects may be remarkably well tolerated. Depending on degree, duration, and cause, valvular stenosis or insufficiency often produces secondary changes in the heart, blood vessels, and other organs, both proximal and distal to the valvular lesion. Most important are the myocardial hypertrophy and pulmonary and systemic changes. Moreover a patch of endocardial thickening often occurs at the point where a jet lesion impinges such as the focal endocardial fibrosis in the left atrium secondary to a regurgitant jet of mitral insufficiency.

Valvular abnormalities may be caused by congenital disorders or by a variety of acquired disease. Most frequent are acquired stenoses of the mitral and aortic valves which account for approximately two thirds of all valve lesions. Valvular insufficiency may result from either intrinsic disease of the valve cups or damage to or distortion of the supporting structures (e.g.,) the aorta , mitral annulus, tendinous cords, papillary muscles, ventricular free wall) without primary changes in the cusps. It may appear acutely with infective endocarditis or chronically with leaflet scarring and retraction. In contrast, valvular stenosis almost always is due to a primary cuspal abnormality and is virtually always a chronic process.

In contrast to the many potential causes of valvular insufficiency, only a relatively few mechanisms commonly produce acquired valvular stenosis. The most frequent chronic causes of the major functional valvular lesions are as follows:

Mitral stenosis-rheumatic heart disease
Mitral insufficiency-myxomatous degeneration (mitral valve prolapse)
Aortic stenosis ? calcification of anatomically normal and congenitally bicupspid aortic valves
Aortic insufficiency ?dialation of the ascending aorta related to hypertension and aging.