Background: Climate change has heightened the threat of heat stroke in previously temperate zones. Aims: This study aimed to assess the outcome of patients in relation to mortality and the role of effect modifiers among heatstroke patients presenting to a tertiary care hospital in Karachi during June 2015. Methods: A retrospective observational study was conducted on heatstroke patients 20-27 June 2015 at the Emergency Room(ER) of a private hospital in Karachi, Pakistan. Patients' demographic data, disease severity, presentation and outcomes were determined. Statistical data was reported as numbers, percentages and mean +/- SD. Results: In total, 315 patients reported to ER; 76.6% patients survived, 23% expired. Males were 55% and 60% patients were fully mobile. Hypertension was the most frequent concurrent disorder. Fever documented in 79.4% and CNS derangement in 73.3% patients were the top most presenting features. Fever and disease severity were found to exert significant impact on disease outcome. Mortality rate dropped from 26 June onwards from 24.35% to 15.9% by using evaporative cooling technique combined with air conduction and maintaining room temperature at 22-24 degrees C. Conclusions: Poor outcome during heatstroke can be minimized by advance planning and timely intervention in lowand middle-income countries.