Phonocardiographic, cardiac catheterization and surgical data are analyzed and compared for six patients exhibiting mitral stenosis whose phonocardiographic findings failed to predict the mitral valve area as estimated by the other two methods. The corrected Wells' indices (Q1 minus 2 OS times) ranged from -5 to +1 and were discrepant to actual valve size in all six patients. Analysis of Q1 and 2 OS intervals usually permits a reasonable estimate of the degree of stenosis of the mitral valve. However, the intervals are altered primarily by pressure changes. Alterations of other factors such as flow, valve stiffness, and regurgitation may result in discrepancies of these measurements. As demonstrated in these patients, the Wells' index is not an absolute criterion of the severity of mitral stenosis.