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Several studies have reported that regular physical activity is an important component of a healthy lifestyle and low levels of physical fitness are closely related to several chronic diseases, including type 2 diabetes mellitus (T2DM). Many studies have also suggested beneficial effects of regular exercise in preventing sudden cardiac death in healthy individuals and in patients with cardiovascular disease. Despite this, there is widespread tendency to ignore exercise testing in clinical management of patients with diabetes mellitus even when evidence abound showing that exercise improves health status in patients with diabetes mellitus (George & Russell, 2007). A very serious and common complication of T2DM is diabetic autonomic neuropathy (DAN). Cardiac autonomic neuropathy is the most clinical important and well-studied form of DAN, due to its association with a wide spectrum of adverse cardiovascular outcomes (Vinik et al, 2003). It is commonly perceived that a regular heart beat is a sigh of healthy heart. However, the rhythm of a healthy heart is characterized by significant beat to beat variability. This heart rate variability (HRV) has been used as a simple, non-invasive technique to examine cardiovascular autonomic function. HRV of 15 individuals with T2DM were assessed. Resting electrocardiogram (ECG) at spontaneous respiration was recorded for 5 min in supine position. Recording was performed before and after a six month, supervised, progressive, aerobic training program, three times weekly. The data were expressed as median (interquartile range). The p value <0.05 was considered statistically significant. In the time domain variable square root of the mean of the squared R-R intervals (RMSSD) [29.7 (26 - 34.5) vs. 46.4 (29.8 - 52.2) ms, p=0.02] and number of R-R intervals that differ by more than 50 ms (NN50) [35 (18 - 47) vs. 98 (20-114)] count, p=0.03) were significantly increased after exercise. In the frequency domain variables low frequency (LF) [62.4 (59.1 - 79.2) vs. 37 (31.3-43.3) nu, p=0.03) and LF/HF [1.67 (1.44 - 3.8) vs. 0.58 (0.46 - 0.59) p=0.009] were significantly decreased while high frequency (HF) [95 (67-149) vs. 229 (98-427) power, p=0.006] and HF [37.6 (20.8-40.9) vs. 63 (56.7-68.7) nu, p=0.003) were significantly increased after exercise. In Poincare plot standard deviation (SD) 1 [21.3 (18.5-24.8) - 33.1 (21.5 - 37.2), p=0.027] was significantly increased after exercise. These data suggest that three times weekly, six month, moderate aerobic exercise program is associated with significant improvements in cardiovascular autonomic function in person with T2DM by increasing vagal tone and decreasing sympathetic activity. [ABSTRACT FROM AUTHOR]