BACKGROUND: We investigated the effect of cardiovascular autonomic neuropathy for left ventricular function in cardiovascular symptom-free type 2 diabetic patients without other major risk factors known to cause cardiac dysfunction, especially diastolic dysfunction. METHODS: Forty seven patients (M:F=20:27, 53+/-10 years) with type 2 DM were enrolled in this study. None of the subjects had the macrovascular diabetic complications, hypertension, hypertrophic cardiomyopathy, valvular heart disease, alcoholic heart disease, congenital heart disease and older age (> 65 years). The patients were tested for cardiovascular autonomic neuropathy using five non-invasive tests of autonomic function. The response to each test was graded as 0, 0.5, 1. A patient was classified as having definite cardiovascular autonomic neuropathy if total score was 2 or more. Using these criteria, 26 patients (Group A) were determined to have cardiovascular autonomic neuropathy. Others were 21 patients (Group B). Tc-99 m RBC gated blood pool scintigraphy was performed as routine standard protocol. RESULTS: The degree of age, sex, body mass index (BMI), duration of diabetes, level of insulin, C-peptide, fructosamine, fasting plasma glucose, total cholesterol (TC), triglyceride (TG), HDL, LDL, BUN, creatinine and incidence of retinopathy, microalbuminuria were not different between group A and B. Heart rate response to Valsalva maneuver, heart rate response to standing were different between Group A and B (p=0.008, p=0.001, respectively). Ejection fraction of left ventricle were normal (> 50%) in all of patients. Maximal filling rate, average filling rate, maximal ejection rate and average ejection rate were increased in patients with cardiac autonomic neuropathy (p=0.03, p=0.05, p=0.02, p=0.04, respectively). Total score of autonomic function was significantly correlated with maximal filling rate (r=0.38, p=0.01), with average filling rate (r=0.37, p=0.01) and with maximal ejection rate (r=0.37, p=0.01). Maximal filling rate was most correlated with resting pulse (r=0.58, p<0.01). CONCLUSION: Cardiovascular autonomic neuropathy as single factor may result in diastolic dysfunction of left ventricle in cardiovascular symptom-free type 2 diabetic patients without other major factor known to cause cardiac diastolic dysfunction.