In this study, we adapted Star-Oddi micro-HRT (G2) bio-loggers for improved function in the cold-adapted Arctic key species Polar cod (B. saida) that generally displays a very low heart rate (ƒH) of 8bpm. To integrate ƒH data with oxygen consumption rates (MO2), we conducted critical swim speed (Ucrit) tests in a swim-tunnel respirometer within the ecologically relevant temperature range of 0–8°C. A significant correlation (p < 0.01) of observed cardiorespiratory parameters indicated primary dependency of ƒH and MO2 during acute warming, suggesting a species-specific potential of ƒH as a proxy for energy expenditure. Despite present Ucrit (2.3 ± 0.3 BL/s) being 20% lower than in untagged conspecifics at similar temperature, maximum metabolic rates were 35% higher for bio-logger-bearing individuals. Apparent excess potential to increase MO2 suggests that polar cod’s performance limitations are not dictated by the absolute capacity of oxygen supply. Hence, alternative explanations determining Ucrit, such as behavioral termination of swimming trials to save energy, or potential limitations in ATP supply to the muscle, are discussed. Heart rate was significantly impacted by both temperature and swimming velocity (p < 0.0001, respectively). Past the optimal temperature range of polar cod (2.8–4.4°C), heart rate ceased to increase, with incremental Q10 values levelling off from 2.63±0.43 at 0–2°C, to 1.73±0.74 at 6–8°C. Consequently, potential impacts of insufficient heart rate scaling with acute temperature rise are discussed in the light of projected Arctic warming.