Why does your heart rate increase in a hot tub?

In a hot tub, the high water temperature causes your body to heat up, leading to vasodilation, which is the widening of blood vessels. This process increases blood flow to the skin to help dissipate heat, resulting in a higher heart rate to maintain adequate circulation and regulate body temperature. Additionally, the warm water can relax muscles and reduce stress, which may also contribute to a slight increase in heart rate.