Introduction & Objective: Hemodynamic Changes in open heart surgery, especially during transfer to intensive care unit (ICU) and in the early hours of stay in ICU is very common. The most common cause of hypotension in the intensive care unit after surgery is the reduction of intravascular volume, so that appropriate compensation and adequate intravascular volume after separation from cardio pulmonary bypass is very important. The aim of this study is to compare the effects of gelatin 4%, voluven 6% and Ringer solution to maintain hemodynamic status after cardiopulmonary bypass in patients undergoing coronary artery bypass surgery. Materials & Methods: In this randomized double blind clinical trial, 92 patients who were candidate for on-pump Coronary Artery Bypass Graft were put randomly in three groups. The first group received Ringer solution, the second group Gelatin 4%, and third group Hydroxy Ethyl Starch 6% (Voluven). Hemodynamic parameters like heart rate, mean arterial pressure, systolic blood pressure, diastolic blood pressure, central venous pressure, cardiac output, urine output and the presence of arrhythmias all were documented for the first 24 hours after operation. One-way ANOVA or its non-parametric equivalent, chi square and Fisher’s exact test, were used for statistical analysis. Results: The volume of solutions that was needed for keeping normal pressure and keeping central venues pressure in the range of 7 to 14mmHg and adequate blood pressure, at the time of surgery during the first 24 hours of stay in ICU was significantly less in the group using voluven 6% than Gelatin and Ringer groups (P-Value = 0.001), but there was no significant difference between Ringer and Gelatin group. Urine volume in the first 4 hours as well as 24 hours stay in Intensive Care Unite in group Voluven was more than Gelatin and Ringer groups (P-Value = 0.03). The mean serum creatinine level were significantly lower from other groups (P-value = 0.004). Conclusions: Hydroxyl Ethyl Starch 6% has better volume expanding effect than Gelatin 4% and ringer and its short-term effects on renal function is also better than other solutions.