Barley, a vital crop globally, faces increasing threats from rising temperatures and climate variability. The physiological and morphological characteristics of ten advanced barley lines and two cultivars were studied in this study over a two-year period under rain-fed conditions. The research revealed significant variations in genotype performance under terminal heat stress. The results highlight that temperature stress exceeded critical thresholds during critical growth stages, impacting grain yield and quality. Genotypes like "IBON HI 16-12" displayed consistent high yields, while "Kendal" showed adaptability across varying conditions. Leaf chlorophyll content (SPAD) and Normalized Difference Vegetation Index (NDVI) values varied among genotypes, and a high NDVI did not consistently lead to higher yields under heat stress conditions. Quality traits, including protein content, test weight, and thousand kernel weight, fluctuated independently of yield. Canopeo measurements highlighted rapid ground cover growth, emphasizing its importance for plant productivity. Genotypes with delayed heading and prolonged physiological maturity exhibited high yields under heat stress. LAI measurements may aid in selecting heat-tolerant genotypes. Alternatively, Canopeo measurements at 85-95% coverage provide valuable data for assessing genotype performance. This study enhances our understanding of barley's response to heat stress, emphasizing genotype adaptability and the need for further research to address temperature-related yield variations.