Tomato (Solanum lycopersicum L.) is economically important worldwide, particularly in tropical and subtropical regions, and is significantly affected by climate change, notably heat stress. This study evaluated the effects of heat stress on root and shoot morphology, photosynthesis, fruit set, and yield traits in five tomato genotypes to identify the characteristics that differentiate heat tolerance from susceptibility, which will enable us to identify sources for key traits for breeding. The heat stress experiment was conducted during the summer under naturally high temperature conditions in a polyhouse, while non stress trail was conducted during winter under comparable natural conditions in polyhouse. Significant differences were observed between the trails and among genotypes, with heat tolerant MG785-1, CLN1621L demonstrating superior root system architecture, greater leaf area and better physiological performance compared to susceptible genotypes like CLN3961D. Root dry weight and root to shoot ratio were key indicators for heat tolerance, while the photosynthetic rate was critical for maintaining plant growth under stress. These findings highlight the importance of strong root systems and effective photosynthesis for heat tolerant tomato, providing new insights into improving crop resilience for regions affected by climate change A germination trial using the paper roll method was also conducted under controlled conditions at 25°C (control) and 36°C (heat stress) 25 APSA lines, However, the results from the germination trial were not statistically significant and did not provide clear insights into genotypic performance under stress.