The aim of this study was to evaluate the use of intraventricular dispersion of the peak diastolic flow velocity as a marker of left ventricular diastolic dysfunction in patients with atrial fibrillation. Regional diastolic flow velocity patterns at 1, 2, and 3 cm away from the mitral tip toward the apex were simultaneously recorded with the mitral flow velocity pattern by using pulsed Doppler echocardiography in 24 patients with atrial fibrillation before electrical or medical cardioversion. Echocardiographic examination was repeated after 10 to 30 days (ie, at the time of recovery of left atrial mechanical functions) after cardioversion of atrial fibrillation in all patients. Thirteen patients were found to have diastolic dysfunction; the remaining 11 patients with a normal E/A ratio constituted the control group. Afterward, the data recorded before the cardioversion were analyzed for each patient. In subjects with normal diastolic function, the peak diastolic flow velocity (PDFV) at the mitral tips also was maintained at the positions 1 to 3 cm away from the tip in the left ventricular cavity (PDFV at the mitral tips: 0.84 m/s, PDFV at 3 cm: 0.85 m/s; P =.34). In contrast, the regional PDFV progressively decreased toward the apex in patients with diastolic dysfunction (PDFV at the mitral tips: 0.82 m/s, PDFV at 3 cm: 0.63 m/s; P =.0004). Only 77% of the initial velocity was maintained at 3 cm away from the mitral tips in patients with diastolic dysfunction, whereas almost 100% of the initial velocity was preserved in patients with normal diastolic function (P <.001). These findings suggest that the assessment of the intraventricular decrease in mitral PDFV may be used as a reliable marker of diastolic dysfunction in patients with atrial fibrillation.