In order to evaluate the heat tolerance of 11 wheat cultivars, an experiment was conducted during 2010-2011 under two conditions, normal (normal sowing) and heat stress (late sowing), in a randomized complete block design with four replications, in Ahvaz climatic conditions. Traits including chlorophyll content, stomatal conductance and cell membrane thermostability were estimated and also STI, HM, MP, GMP, SSI, TOL, YI and YSI indices were calculated based on grain yield in this research. Stress intensity (SI) equal to 0.59 which is indicative of a relatively severe stress was estimated in this experiment. The results showed a significant difference among genotypes for all traits. The stomatal conductance of heat tolerant cultivars increased significantly under heat stress. This showed the importance of this trait in acclimation of cultivars to heat stress. This trait has the potential to be used for screening the genotypes against heat. The highest quantity for stomatal conductance, 0.59 molm-2s-1 was recorded for Kauz as a tolerant cultivar. Although cultivars showed significant difference for cell membrane thermostability, this trait was not detected as a suitable trait for evaluating the heat tolerance of cultivars. No significant differences were observed for chlorophyll content under normal and heat stress conditions. The average of yield under normal and heat stress was detected as 6381 and 3769kg ha-1 respectively. STI, HM, MP and GMP indices were selected as the best indices based on the correlation with grain yield under normal and heat stress conditions. Results showed that Kauz and Chamran were tolerant cultivars to heat stress and had high performance under normal and heat stress conditions. In contrast, Montana, Niknejad, M6 and Durum-ch-89 cultivars were susceptible to heat stress and had low performance under both normal and heat stress conditions.