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Echocardiograms showing mitral valve leaflets, interventricular septum, and posterior wall of the left ventricle simultaneously were recorded at a paper speed of 100 mm/s in 20 normal subjects. These records were manually digitized and a computer was used to derive mitral valve velocity, left ventricular dimension, and its rate of change continuously throughout a single cardiac cycle. The pattern of instantaneous mitral valve velocity with respect to time was similar in all subjects studied, showing a peak opening rate of 400 +/- 60 mm/s (mean +/- 1 SD), and continuously changing velocity throughout the period of mid-diastolic closure. The peak diastolic closure rate was 250 +/- 60 mm/s and thus appreciably higher than average velocities obtained by manually measuring the slope. A close time relation existed between mitral valve and left ventricular wall movement in early diastole. Forward movement of the anterior leaflet began 1 +/- 6 ms after the onset of outward wall movement, and peak velocity was reached 2 +/- 7 ms after the maximum rate of change of dimension. Later, a discontinuity in wall movement at the end of rapid filling preceded a corresponding discontinuity in the mitral valve velocity tracing by 5 +/- 10 ms. The technique, therefore, allows continuous measurement of mitral valve velocity, and demonstrates its close relation to left ventricular wall movement during diastole.