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Introduction: Occupational heat stress can lead to cardiovascular and thermoregulatory changes, including elevated heart rate, increased core temperature, and altered blood pressure. Evidence remains limited regarding the physiological impact of heat stress in tropical occupational settings. Sugarcane workers in Thailand experience prolonged exposure to extreme heat during harvesting. This study assessed the impact of heat stress exposure on physiological responses among Thai sugarcane workers. Methods: Field measurements were conducted in Nakhon Sawan Province during cooler and hotter harvesting periods in 2023. Demographic, health, and work-related data were collected using a questionnaire. Heat stress exposure was assessed using Wet Bulb Globe Temperature (WBGT) across entire shifts, and a full work shift time-weighted average effective WBGT (WBGTeff-FS-TWA), adjusted for clothing, was calculated. Resting heart rate, body temperature, and blood pressure were recorded pre- and post-shift. Associations between WBGTeff-FS-TWA and post-shift physiological parameters were analysed using general linear regression, adjusting for pre-shift values and confounders. Results: Mean WBGTeff-FS-TWA was 31.3 ± 2.8 °C (range: 22.9–35.4 °C). Post-shift systolic and diastolic blood pressures were significantly lower, while heart rate and body temperature were significantly higher compared to pre-shift values (p < 0.001). WBGTeff-FS-TWA was not associated with post-shift blood pressure. However, heart rate increased by 0.61 beats/min (95% CI: 0.24–0.98) and body temperature by 0.02 °C (95% CI: 0.002–0.03) per 1 °C increase in WBGTeff-FS-TWA. Conclusion: Heat stress exposure was linked to modest increases in heart rate and body temperature among sugarcane workers. With rising global temperatures, monitoring cardiovascular and thermoregulatory responses is critical for safeguarding workers in hot environments.