The present investigation was carried out at El-Mattana Agricultural Research Station, Agricultural Research Center, Egypt, during the seasons 2017/2018 and 2018/2019. Seven diverse cultivars of wheat (Triticum aestivum L.) namely, Gemmeiza 11, Misr 1, Sids12, Giza 171, Sakha 93, Shandaweel 1 and Sids13 and their 21 F₁ hybrids were sown in two sowing dates to study the effect of heat stress on gene action of yield and its components i.e. number of spikes/ plant,biological yield/plant, number of grains/spike, grain yield/plant, 1000-grain weight, harvest index andstraw yield /plant under both conditions. The differences among genotypes, parents, crosses, and parents versus crosses were highly significant under both conditions for most studied traits. Highly significant differences due to general (GCA) and specific (SCA) combining abilities were detected for all assessed traits in both environments as well as the combined analysis. GCA/SCA estimates were less than unity in most of the study traits in each environment and combined analysis. Results showed that both additive and non-additive types of gene effects were affected by planting date conditions. Five parents (P_5, P_4, P_7, P₁ and P₆) gave highly significant positive GCA effects for biological yield /plant, number of grains/spike and harvest index traits under both conditions. Six crosses P₁ × P₃, P₁ × P₆, P₁ × P₇, P₃ × P₄, P₃ × P₅ and P₅ × P₆ had highly significant SCA effects under both conditions. The estimates of heterosis showed that there were positive and significant or highly significant heterotic effects over better parent under normal and late sowing dates in all studied traits and were recorded for no. of spikes/plant (6 and 17 crosses), biological yield/plant (7 and 21 crosses), no of grains/spike (6 and 6 crosses), harvest index (8 and 3crosses) and straw yield/plant (7 and 19 crosses) respectively. Four crosses (P₂ × P₄), (P₄ × P₅), (P₄ × P₆) and (P₄ × P₇) including Giza 171 (P₄) have heat susceptibility index (HSI) values less than unity. This indicates that the tolerant parent (P₄) transmitted its genes controlling tolerance to heat stress to its hybrids. Such results cleared that high-temperature stress caused a reduction for all studied traits.