Acute heat episodes (heatwaves) present some of the most significant challenges for plants growing in both natural and agricultural settings. Circadian systems are molecular time-pacing mechanisms responsible for synchronizing a wide range of rhythmic physiological processes with the appropriate time of day. We hypothesized that the circadian system may contribute to the capacity of wild barley plants to withstand extreme heat events. We have used chlorophyll fluorescence to analyse circadian rhythms in a panel of wild barley (Hordeum spontaneum) accessions from diverse environmental sites across the Southern Levant in response to heat wave conditions. Average linear multi-models have been constructed to find correlations between rhythm attributes and eco-climate at the sites of origin of the accessions. Under optimal conditions, the environment explained a significant portion of the variance in period time and amplitude. By contrast in heat wave conditions despite a mean shortening of period and decrease in amplitude, circadian traits did not correlate with eco-climate origins. Circadian flexibility appears to be more important. We show that plant vitality in acute heat stress is correlated with circadian plasticity in response to increasing temperatures and examine whether acute heat stress resilience in wild barley is predominantly associated with specific eco-climate origins.