In our study, the adaptive potential of Mytilus edulis L. mussels of different ages under temperature changes was for the first time evaluated using the method of remotely recording animal cardiac activity. It showed that mussels with a shell size of 40–50 mm (age 6+) had the ability to adapt to higher temperatures compared to younger and older mollusks. The variance of heart rate indicators declined when reaching critical temperatures along the mussel size gradient from 10 to 70 mm. The heart rate drop at critical temperatures was more pronounced in young (2+ – 5+) and old animals (7+ – 9+) compared to 5–6-year-olds. Our results suggest that these mussels are the most adaptable to temperature changes. In addition, the adequacy of the technique of remotely controlling the cardiac rhythm in mollusks for assessing their temperature adaptation potential has been experimentally proven.