BACKGROUND AND OBJECTIVE: Mechanical ventilation affects heart and hemodynamic function. Nitroglycerine (NG) and Na Nitroprusside (NPS) are used to apply as deliberate hypotension by decreasing the preload and afterload of heart, respectively. This study was evaluated the effects of different tidal volumes on a few hemodynamic components during these kinds of controlled hypotension. METHODS: In a double-blind clinical trial, 60 anesthesia patients were randomly selected during mechanical ventilation with different tidal volumes (5, 10 & 15 cc/kg) for ten minutes before and after controlled hypotension which induced by NG or NPS. Changes of some hemodynamic components were measured and analyzed. FINDINGS: Before hypotension, the cardiac output (CO) decreased from 3.35±0.35 to 3.05±0.65 and from 3.51±0.34 to 3.06±0.56 lit/min in NG and NPS groups, respectively (p<0.000) and stroke volume (SV) decreased from 35.26±3.43 to 17.42±4.36 and 36.28±3.04 to 18.71±5.05 cc respectively (p<0.000) by increasing the tidal volume from 5 to 15 cc/kg. During controlled hypotension by increasing the tidal volume from 5 to 15 cc/kg, the CO decreased from 2.84±0.73 to 2.57±0.64 in NG group and increased from 4.26±0.56 to 4.57±0.81 lit/min in NPS group (p<0.000) and SV decreased from 15.86±4.62 to 13.46±4.29 in NG group and enhanced from 18.75±5.52 to 19.58±5.42 cc in NPS group (p<0.028). CONCLUSION: The results of this study showed that the cardiac output was decreased by increasing the tidal volume during mechanical ventilation and controlled hypotension by NG while it was increased in NPS group. The decrease of stroke volume in NG group was greater than NPS group by increasing the tidal volume.