Understanding variation in physiological adaptations to thermal stress is vital when investigating intertidal species’ distribution patterns. The thermal sen- sitivities of two limpets, Cellana grata and C. toreuma, differed in accordance with their vertical distributions. Cardiac performance was maintained at higher tempera- tures (*47°C) for the high-zone C. grata than the mid- zone C. toreuma (*42°C). At 40°C, C. grata maintained regular heart function for *4 h, while heart function of C. toreuma decreased rapidly. Heat shock protein expres- sion revealed that C. toreuma had two constitutive iso- forms, Hsp77 and Hsp72, and C. grata one inducible form, Hsp75, which was upregulated at 40°C, suggesting C. grata has a more effective heat shock response than C. toreuma. The temperature-adaptive differences in cardiac thermal tolerance and Hsp expression match observed differences in thermally induced mortalities with the onset of summer and may help predict differential effects of climate change on the two congeners.