Left ventricular (LV) diastolic functions in 23 patients with aortic regurgitation (AR) and 22 patients with mitral regurgitation (MR) were evaluated by gated pool scintigraphy. LV myocardial biopsy was performed during open heart surgery, and LV myocardial ultrastructural chasges were evaluated by electron microscope. Correlation between LV diastolic function and myocardial ultrastructural change was examined. It was suggested that preoperative LV diastolic dysfunction occurred earlier than LV systolic dysfunction in patients with AR and MR. LV early diastolic dysfunction was especially significant in patients with AR. LV systolic function was significantly improved postoperatively compared with LV diastolic function in patients with AR and MR. It was suggested that LV interstitial fibrosis caused LV diastolic dysfunction in patients with AR and MR, and insufficiency of myocardial thickening as compensation in patients with MR. It was presumed that LV diastolic dysfunction was irreversilble in patients with AR and MR in the distant postoperative period due to persistence of the preoporative myocardial ultrastructural change, e.g, interstitial fibrosis. these LV diastolic indices measured by gated pool scintigraphy were useful in predicting LV ultrastructural changes and postoperative LV dysfunction in patients with LV volumeoverloaded valvular heart disease.