Doppler left ventricular (LV) inflow is reportedly affected by LV diastolic properties. We evaluated 48 subjects consisting of 27 patients with chronic mitral regurgitation (MR) and 21 patients with noncardiac disorders who received echocardiographic examinations. The deceleration rate divided by diastolic dimension (DR/Dd) derived from Doppler early diastolic LV inflow was correlated with the peak diastolic velocity divided by diastolic dimension (peak DV/Dd), a conventional index of LV diastolic function derived from the M-mode echocardiogram in the 48 patients, regardless of the presence of normal sinus rhythm or atrial fibrillation. LV diastolic function was then estimated by comparing perioperative echocardiographic examination and LV micro-and ultrastructural findings of biopsy specimens from 12 patients with MR who received mitral valve replacement. Fiber diameter, volume fraction of interstitial fibrosis (int. % Fib), and volume fractions of three intracellular components; the myofibrils (% MF), the sarcoplasmic reticulum (% SR) and the mitochondria (% MT), were measured in LV transmural biopsy specimens. DR/Dd was significantly correlated with peak DV/Dd before and after operation. Peak DV/Dd and DR/Dd were inversely correlated with int. % Fib and % SR, and were positively correlated with % MF. We subdivided the 12 MR patients according to their postoperative DR/Dd values as "recovered", and "non-recovered" based on their postoperative LV diastolic function. % MF was significantly lower in the 'non-recovered' group. Thus, DR/Dd can serve as an index of LV diastolic function. A decrease in % MF may inhibit the recovery of postoperative LV diastolic function.