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High values of temperature and ozone (O-3) concentrations often coexist revealing the strong relationship between them. In this study, we examine the O-3-temperature slopes for two heatwave episodes during the summers of 2003 and 2014 in Europe. In both heatwave episodes, similar slopes of about 3.1ppb/degrees C are found, about 1ppb/degrees C higher when compared with summers with near normal temperatures. The lowest correlation coefficient calculated for the two variables in the 2003 heatwave is attributed to the break of the O-3-temperature relationship in the higher percentiles of both variables, while for the 2014 heatwave the highest correlation coefficient is attributed to the increased isoprene emission fluxes. However, the clear response of O-3 to temperature perturbations in 2003 was better manifested when the mean anomalies of the two variables between the heatwave and the normal period were examined, with the calculated slope of about 4.75ppb/degrees C. In addition, the slope of about 1.5days of O-3 exceedances/day with T-max>90th percentile indicates the role of extreme temperatures to the extension of the O-3 exceedance period. This indicates that when future O-3 levels are estimated based on the relationship of O-3 with meteorological variables (such as temperature), extreme periods (such as heatwaves) should be taken into account in their training periods in order to obtain more realistic results.