The association between left ventricular diastolic dysfunction and myocardial MIBG accumulation was investigated. The subjects were 14 Type II diabetic patients who had no evidence of ischemic heat disease, LV hypertrophy or dilated cardiomyopathy as determined by exercise T1-201 myocardial scintigraphy and echocardiography. In 14 diabetic patients, isovolumic relaxation time (IRT) was measured by M-mode echocardiography, and the subjects were subdivided into two groups: Group 1, 8 patients with impaired left ventricular diastolic function (IRT≥80 msec), and Group 2, 6 patients with normal left ventricular diastolic function (IRT<80 msec). 123I MIBG myocardial scintigraphy was performed, and the myocardial accumulation of 123I MIBG was investigated. The ratio of myocardial to mediastinal MIBG uptake was significantly (p<0.01) lower in Group 1 than in Group 2. And scintigraphic defects were significantly (p<0.05) more numerous in Group 1 than in Group 2. Patients in Group 1 had a greater frequency of cardiac autonomic neuropathy evaluated by QTc interval and coefficient of variation of R-R interval, when compared with Group 2. These data suggest that, in diabetic patients with no evidence of ischemic heart disease, LV hypertrophy or dilated cardiomyopathy, impairment of left ventricular diastolic function is associated with cardiac autonomic neuropathy.