The purpose of this study was to investigate the independent association between global cardiac autonomic neuropathy (CAN) and left ventricular (LV) dysfunction in addition to regional associations of LV dysinnervation and function, in patients with type 2 diabetes mellitus (T2DM).CAN represents a potential mechanism in the etiology of nonischemic diabetic cardiomyopathy.Clinical measures of CAN based on total spectral power of heart rate variability and cardiac reflex testing and echocardiographic assessment of LV function were performed in 118 patients with type 2 diabetes mellitus. Systolic and diastolic function were defined at rest and peak exercise using peak systolic and peak early diastolic (Em) tissue velocities, calculated in 6 basal- and mid-segments using color tissue Doppler. Iodine 123-metaiodobenzylguanidine imaging was performed in 33 patients to directly quantify global (heart/mediastinum ratio) and regional LV sympathetic integrity.Patients with CAN demonstrated higher resting heart rate, systolic and mean blood pressures, aortic stiffness, hemoglobin A(1c), and urine albumin/creatinine ratio, in addition to lower peak heart rate, chronotropic index, and exercise capacity. Diastolic function (Em) was associated with CAN, evidenced by total spectral power (r = 0.42, p < 0.001) and heart/mediastinum ratio (r = 0.41, p = 0.017). Diastolic function (Em) at rest and systolic function (peak systolic tissue velocity) at rest and exercise were significantly reduced in patients with CAN. Furthermore, total spectral power was associated with Em independent of age, hypertension, metabolic factors, and other relevant contributors to LV dysfunction (β = 0.20, p = 0.035). Relative regional tracer deficits indicative of local denervation were predominant in the anterior and lateral walls (p < 0.001). Associations with regional Em, independent of global iodine 123-metaiodobenzylguanidine uptake, were identified exclusively in mid-anterior (β = 0.45, p = 0.01) and mid-lateral walls (β = 0.34, p = 0.03). However, no association was found between regional denervation and systolic or diastolic dyssynchrony.The diastolic dysfunction of type 2 diabetes mellitus shows associations with both regional markers of sympathetic integrity and clinical markers of autonomic neuropathy.