A cross sectional study was conducted to determine the exposure of heat and its effect to physiological changes among male workers in an automotive manufacturing plant in Shah Alam, Selangor. Forty six workers from the foundry operation division in the factory were selected as respondents. Variables measured were the environmental temperature (WBGTin), metabolic workload, body core temperature, and blood pressure, heart rate as well as heart rate recovery. Results showed that the mean of environmental temperature (WBGTin) was 28.960C. These production workers were exposed occasionally to heat during melting process, loading silica and powder into the molds as well as when making core products into the mold. The average time of monitoring was 2 hours for intermittent exposure and 8 hours duration for overall exposure. Bonferonni Test showed significant differences of body core temperature between before the shift starts and 2 hours after the shift started (p = 0.05) and after 8 hours ( p < 0.001) respectively. A weak correlations were found between body core temperature with heart rate before the shift starts (r = 0.293, p = 0.048), and with systolic blood pressure after 8 hours (r = 0.309, p =0.036) respectively. The average heart rate was in range 51 to 98 beat per minute, indicating that there is no excessive physiological demand. The mean of body core temperature (36.37 ± 0.53 0C) and heart rate (74.50 ± 10.10 beap perminute) after 8 hours indicated a good body control of heat exposure. Three out of four work stations monitored had temperatures greater than 28 0C (ACGIH TLV). The workers were exposed to moderate heat stress during the study period; however, body core temperature, heart rate and blood pressure did not reach unacceptable level of physiological strain.