Continuous wave Doppler echocardiography (CWD) is widely used in the assessment of pressure gradients in patients with valvular heart disease, utilizing the simplified Bernoulli equation. However determination of non-simultaneous mean pressure gradient (MG) in mitral stenosis (MS) from CWD recordings has often been described as being unsatisfactory. Therefore, the purpose of this study was to compare the estimates of trans-mitral MG derived from CWD with gradients measured simultaneously at cardiac catheterization (beat to beat analysis). We studied 3 patients (pts) with MS (1 man and 2 women, aged 55, 55 and 62 years respectively); one patient (pt) was in sinus rhythm and 2 were in atrial fibrillation. In each pt the trans-mitral flow velocity curve was obtained simultaneously with trans-mitral gradient measured directly at cardiac catheterization (cath). In this way it was possible to obtain a beat to beat correlation between Doppler and cath in 181 beats taken from the 3 pts. These beats were selected from a total number of 321 beats because of their excellent quality for analysis (74 beats were obtained from the first pt, 38 from the second pt and 69 from the third pt). Mean diastolic velocity, defined as the mean of maximal velocities throughout diastole, was obtained for each beat by planimetring the envelope of the spectral velocity profile. MG was calculated from mean velocity by applying the simplified Bernoulli equation (delta P = 4V2).(ABSTRACT TRUNCATED AT 250 WORDS)