BACKGROUND: In this study, we examined diabetic patients scheduled for elective coronary artery bypass surgery to determine whether there is an association between autonomic dysfunction and intraoperative hemodynamic instability, and if perioperative autonomic function tests are effective predictors for diabetic patients at greatest risk for hemodynamic events during the intraoperative period. METHODS: We examined 52 patients, 25 without diabetes (nonDM group) and 27 with diabetes (DM group). Preoperative autonomic function tests included are the valslava maneuver (valsalva ratio, valsalva index, strain response), change in heart rate with deep breathing (I/E ratio), change in heart rate (30:15 ratio, stress response) and diastolic blood pressure (L-S(d)) while standing. Anesthesia was established with midazolam, fentanyl, isoflurane and vecuronium. Several hemodynamic variables such as heart rate (HR), mean arerial pressure (MAP), central venous pressure (CVP), mean pulmonary artery pressure (MPAP), pulmonary capillary wedge pressure (PCWP), systemic vascular resistance index (SVRI), pulmonary vascular resistance index (PVRI), cardiac output (CO), and cardiac index (CI) were obtained at the following times: before induction; after induction; after intubation; after skin incision and after sternotomy. RESULTS: The DM group had a significantly diminished response compared with the nonDM group in the valsalva ratio, valsalva index, 30:15 ratio, and L-S(d). The remaining tests (I/E ratio, strain response, stress response) showed similar but nonsignificant diminished trend response in the DM group. Most patients had one or more abnormal test results in this group (76%), whereas in the control group most patients did not show any abnormal test results (74.1%). The comparison of hemodynamic response between the DM group and non-DM group reveal a significant difference between times within each group but not between groups. CONCLUSIONS: This study indicates that increased hemodynamic instability during the intraoperative period is not an obligatory association with diabetes and autonomic dysfunction and is not detected bypreoperative autonomic function tests in patients with coronary artery disease and diabetes mellitus when anesthesia is induced and maintained with a large dose of opioid and anesthetic agent which has minimal hemodynamic effects.