Background: Climate change is evident around the globe causing heat stress as an emerging public health problem for people working in tropical and subtropical areas. Occupational heat stress can impact the health and productivity of small and mid-sized enterprise workers. Objective: This study aimed to profile the indoor thermal environmental conditions and modify the working practices by recommending the work/rest cycle according to the international organization for standardization 7243. Study Design: This cross-sectional study design included eight industrial (Iron spare parts manufacturing) small and mid-size enterprises in Lahore, Pakistan. The indoor thermal environment, including globe temperature, natural wet bulb temperature, ambient temperature, relative humidity, and air velocity, were recorded during summer to measure the wet bulb globe temperature (WBGT). Quest heat stress meter (model 2500), modified Testo loggers (177-T4), and EL-USB-2-LCD data loggers were placed at different working stations to measure these thermal environmental parameters. A self-administered questionnaire was used to measure the workers' demographic characteristics and working practices. The International Organization for Standardization 7243 reference was used to estimate and recommend the work/rest cycle. Results: 138 workers aged 28.59 +/- 10.46 years participated in this study. Continuous work of 8.8 +/- 1.5 hours per day with a conventional resting period of 30-60 minutes was recorded on a typical working day. The indoor wet bulb globe temperature ranged from 26.8 degrees C to 36.4 degrees C. The workers were registered for low (72.5%), moderate (18.1%), and high (9.4%) metabolic rates according to the International Organization for Standardization 7243 reference values. Conclusion: A high wet bulb globe temperature was recorded in the selected small and mid-sized enterprises making these workers vulnerable to heat stress and related illnesses. Work/rest cycle evaluation suggested that the workers were required to improve their cool-down time by avoiding continuous exposure to high temperatures and reducing the metabolic rate.