Introduction: Successful cardiopulmonary resuscitation after in-hospital cardiac arrest depends on basic and advanced life support systems, the ability to immediately defibrillate the arrested heart, and the quality of the CPR intervention. Aim: To determine the frequency of different cardiac arrest rhythms during the cardiac arrest event and also their effect on outcome. Methodology: This was a prospective study conducted in patients who sustained cardiac arrest in a tertiary hospital over 20 months. Tools used to collect data were Modified Utstein style Format for standard reporting of In-hospital cardiopulmonary resuscitation and Modified Early Warning Score chart. Results: There were a total of 1135 patients in the Pre MEWS group and there were 820 patients in the Post MEWS group. A total of 279 (14.27%) patients sustained VF/VT, 570 (29.15%) had pulseless electrical activity and 1106 (56.57%) had asystole. Survival to hospital discharge was significantly higher with VF/VT (18.27%) as compared to asystole (7.14%) and PEA (11.75%). There was no difference in the frequency of any cardiac arrest rhythm in various age groups, gender or degree of illness (APACHE II score). Furthermore, the cerebral performance category was significantly better if the initial rhythm was VF/VT. Survival to hospital discharge was higher if the initial rhythm was VF/VT (18.2%) as compared to asystole (7.14%) and pulseless electrical activity (11.75%). In the Pre MEWS period, 8.5% of the patients sustained VF/VT as compared to 23.7% sustaining VF/VT in the Post MEWS period. Conclusion: First monitored rhythm as VF/VT has significant association with the survival. Modified early warning score helps the nurses and the physicians to identify patients at risk of In-hospital adult cardiac arrest and this improves the survival of the patients.