Context: Subarachnoid block (SAB) is a safe anesthestic technique commonly practiced worldwide. It is associated with hypotension (33%), bradycardia (13%), and shivering due to hypovolemia, sympathetic blockade, and Bezold- zarisch reflex. Hypotension is managed with vasopressors and crystalloids, while drugs and physical methods are useful to control shivering. Aims: The study aims to evaluate the efficacy of ondansetron versus low dose ketamine to prevent hypotension and shivering during SAB. Settings and Design: A prospective, randomized comparative study. Methods: The studywas conducted on 120 patients undergoing elective lower abdominal surgeries under SAB. Patients were randomly allocated into two groups of 60 each. Group K received 0.25 mg/kg ketamine, while Group O received 4 mg of ondansetron as a slow intravenous infusion (IV) 5 min before SAB. Mean arterial pressure (MAP) and Heart rate (HR) were studied at 2 min intervals for the first ten minutes and once in 5 minutes for the next thirty minutes. Shivering scores were measured at 5 min interval for 40 min. Statistical Analysis: Mean Arterial pressure and heart rate were compared and analyzed using unpaired t-tests. Shivering was compared using contingency tests. Results: A decrease in HR is significantly lower in group K than in group O after 2 min (p < 0.001), 8 min (p < 0.001), 15 min (p < 0.0031), 25 min (p < 0.0115) and 40 min (p < 0.0037) of SAB. MAP was increased at 2 min time interval in the Ketamine group comparative with the Ondansetron group with a p-value <0.05 showing a high statistical significance. Group K had grade I (p < 0.001) shivering in 70% (42) of the patients compared with 36.7% (22) of patients in group O. Conclusion: Administration of IV ondansetron and ketamine prevents SAB induced hypotension and shivering effectively.