Background: An ideal neuromuscular blocking agent should have a high degree of potency, rapid onset of action and short duration of action. It should not cause haemodynamic changes through releasing histamine, ganglion block, anti-muscarinic effects on heart or sympathomimetic action. This study was designed to compare the effect of cisatracurium with or without magnesium pretreatment on neuromuscular blockade and hemodynamics in cardiac surgery patients on cardiopulmonary bypass with objective to assess and compare intubation conditions and timing of intubation in minutes and assess and compare clinical duration of blockade, haemodaynamics variable and side effect if any. Materials and Methods: Hospital based, prospective, randomized double blind observational study. Total 60 patients included in the study (30 in each group). Group A Pretreatment with mgso 4(50mg/kg BW in 100ml NS 10 mints before general anesthesia (GA) and muscle relaxant injection Cisatracurium 0.2mg/kg. Group B received 100ml NS 10 mints before general anesthesia (GA) and muscle relaxant injection Cisatracurium 0.2mg/kg. Results: The mean onset of action of injection cis-atracurium after intubating dose in group A was 4. 27+/1.68 minutes as compared to 5.48+/-1 minutes in group B(p-value<0.001) which showed that onset of action was significantly less in group A as compared to group B. Duration of action of intubating dose of cisatracurium was prolonged by pre-treatment of Mgso4. Haemodynamic parameters were comparable and there was no statistically significant difference among both the groups. No side effect reported in our study.