“Our heart rate adapts to our body’s need for energy throughout the day, whether it’s for walking up the stairs or a bout of strenuous exercise. These tempo changes based on physical activity are perfectly normal.

Other common situations can trigger changes in heart rhythms too. Mild dehydration can cause the heart to beat more quickly; that’s the body’s way of trying to maintain the flow of blood when there’s less available for every beat.”.

John Hopkins Medicine