Assessment of maximum aerobic scope, as a proxy for scope of activity, in ectotherms can be instrumental in predicting distributional responses to e.g. global warming. The waters of the Arctic regions represent one of the most vulnerable ecosystems to climate change. In this study, we determine the optimum temperature (T_opt) of nine adult Arctic charr (Salvelinus alpinus) from Qeqertarsuaq, Greenland, using maximum heart rate (f_Hmax) for investigating the optimal temperatures for activity. The Arrhenius breakpoint of maximum heart rate measurements occurred between 5.9 and 8.3 °C (average = 7.5 °C ± 0.4). The Q₁₀ breakpoint occurred at an average of 7.1 °C ± 0.3. There was no significant difference between the breakpoint temperature found using Q₁₀ and Arrhenius [two-sample t test, df = 16; p > 0.1]. The highest f_Hmax was found at 12.8 °C ± 1.0 reaching an average of 61.8 BPM ± 3.1. Arrhythmia occurred between 11 and 18 °C (average = 15.2 °C ± 0.9). The results obtained in this study suggest that the studied population of Arctic charr lives at summer temperatures (−0.6 to 9.1 °C) that are optimal for activity, but an increase in temperature expected with climate change, could have an impact on life cycle events and fitness-related tasks for this northern population.