Heat stress has become one of the major constraints in maize production worldwide. The current research was planned to define the heat stress-related characteristics of indigenous and exotic maize hybrids based on morpho-physiological and grain quality traits. The research was conducted at Maize & Millets Research Institute (MMRI), Yusafwala, Sahiwal during spring 2019. Hybrids were sown under two heat regimes: (i) optimal sowing and (ii) sowing under heat stress (late sowing). Hybrids differed significantly (P<0.05) in grain yield and related traits under both conditions. Correlation analysis showed a positive correlation of grain yield with net photosynthetic rate (r = 0.393*), days to 50% anthesis (r = 0.437*) and days to 50% silking (r = 0.429*), and a negative association with ear leaf angle (r = −0.420*) under heat stress. Cluster analysis categorized maize hybrids into three clusters based on their mean performance under optimal and heat stress conditions. It further showed that indigenous hybrids (cluster 3), especially KSC-9663, YH-5519, YH-5482, YH-1898, and YH-5507, were more productive and heat tolerant than exotic hybrids i.e., MV-633, MV-600-4, Maxima, SHG-43, and MV-600-2 (cluster 1). Principal component analysis (PCA) and biplot graphs showed that the first five principal components contributed 72% of the total variability among genotypes and that the main sources of variation were days to 50% anthesis and silking, plant height, percentage of protein, and oil contents, stomatal conductance, and net photosynthetic rate. Manuscript profile