To evaluate left ventricular (LV) diastolic function and potential, LV filling curves for 18 patients with atrial fibrillation (Af) were constructed and their positions and appearance were evaluated quantitatively by analysis of 95% maximal filling volume points and maximal curvature alteration points. The LV filling curves of group A (Af only) lay left superiorly, while those of group B (impaired LV diastolic function) were situated right inferiorly, all bending steeply. The LV filling curves of group C (mitral stenosis) bent slightly. The lowest normal filling volume points and compensation areas were calculated to evaluate LV diastolic function and were demonstrated to be very different in groups A and B. The lowest normal filling volume points of group C were similar to those of group A, but compensation areas were smaller, indicating a lower LV diastolic potential. It is concluded that the 95% maximal filling volume point, maximal curvature alteration point, lowest normal filling volume point and compensation area are effective indices for evaluating not only LV diastolic function but also the diastolic potential.