The left ventricular relaxation period has been studied by digitized monodimensional echocardiography in 14 patients with symptomatic pure mitral stenosis and in 11 normal subjects. The maximal relaxation rate and the maximal circumferential relaxation rate differed significantly in both groups (p less than 0.001) with a marked reduction in the patients with mitral stenosis; it was, however, not possible to trace a significant correlation between mitral valve area and the indices of diastolic phase, excepted a slightly significant one for the mean relaxation rate (r = 0.7). In spite of the fact that these results show a delayed left ventricular filling in mitral stenosis, the correlation with the mitral valve area was poor and suggests that it is not satisfactory to estimate the left ventricular filling only by the variation of the ventricular transverse diameter, and that a more accurate evaluation of the mitral valve area should include, in addition to the measurement of the ventricular relaxation rate, at least an indirect estimation of the transmitral pressure gradient, for instance by Doppler echocardiography of the transmitral flow.