Background. Restrictive or pseudonormalized mitral flow velocity pattern (MFVP) is observed not only in patients with heart failure but also in patients with severe mitral regurgitation (MR). It is important to assess the restrictive MFVP which is primarily due to functional deterioration of the left ventricle or due to MR in individual patients. We hypothesized that left atrial (LA) geometry may be used to estimate restrictive MFVP due to heart failure or MR.Methods. In addition to MFVP and LA chamber size, LA eccentricity index was determined as LA superior-inferior dimension x2/(LA antero-posterior dimension + LA medio-lateral dimension) using 2-dimensional echocardiography in 61 sinus rhythm patients with LA volume of 35 ml or greater. Ten patients had congestive heart failure (CHF group), and 9, severe organic MR (MR group). LV diastolic dysfunction was the most likely explanation for the LA enlargement in the remaining 42 patients (DDF group).Results. There was no difference in mitral E/A ratio (peak early diastolic flow velocity/peak flow velocity at atrial contraction) or in LA chamber size between the MR and CHF groups, but the LA eccentric index was greater in the CHF and DDF groups than in the MR group indicating that LA geometry was spherical in the MR group and elongated in the CHF and DDF groups.Conclusions. Two-dimensional echocardiographic assessment of the LA geometry is useful to determine whether the pseudonormalized or restrictive MFVP is due to functional deterioration of the left ventricle or due to MR. (J Echocardiogr 2005; 3: 109-117)