Cardiovascular autonomic neuropathy is the most frequent clinical form of autonomous diabetic neuropathy and appears secondary to cardiac autonomous fibre involvement, actively involved in cardiac rhythm impairment. Type 2 diabetes mellitus patients can present cardiac autonomic neuropathy early in the disease. Autonomous nerve function in DM patients should be assessed as early as the diagnosis is set in order to establish the optimal therapeutic strategy. The most frequent cardio-vagal test used is heart rate variability. An abnormal heart rate variability in the presence of orthostatic arterial hypotension indicates a severe cardiac autonomic neuropathy diagnosis. The development of cardiac autonomic neuropathy is subjected to glycaemic control, duration of the disease and associated risk factors. The glycaemic control is extremely important, especially early in the disease. Therefore, a poor glycaemic control carries unfavourable long-term effects, despite an ulterior optimal control, a phenomenon named “hyperglycaemic memory”. In type 2 diabetes mellitus patients, the association of cardiac autonomic neuropathy with intensive glycaemic control increases the mortality rate, due to the fact, that, secondary to autonomous impairment, the patients do not present the typical symptoms associated with hypoglycaemia. Stratifying the cardiac autonomic neuropathy aids the clinician in assessing the morbidity and mortality risk of diabetes mellitus patients, because it is an independent risk factor for mortality, associated with silent myocardial infarctions and the risk of sudden death.