According to Life123, temperature affects heart rate in ectothermic organisms because they depend on their environment and temperature-controlling systems to determine their own temperature and heart rate. In general, colder temperatures result in lower heart rates and warmer temperatures result in higher heart rates.
Ectothermic organisms move slowly early in the morning. The organism's body temperature is cooler in the morning, which causes its heart rate to be slower. This is due to the cooler atmospheric temperatures the organism is exposed to during the night. As the day moves on, and atmospheric temperatures rise, the ectothermic organism's heart rate increases as the organism's temperature increases. As a result, the ectothermic organism moves around more during the day while temperatures are warmer, notes Life123.
Life123 states that it is hard for ectothermic organisms to regulate their body temperature. It is much more complicated than simply sitting in the sun to warm up or sitting in the shade to cool down. The environment is the leading factor in controlling the temperature of ectothermic organisms. When the weather is not suitable for these organisms, many of them use behavioral techniques to help control their body temperature since these types of organisms do not sweat.