Increase of heart beat while stepping up stairs.....

Please meet a doctor immediately.

Heart beat increases with intensity, when you are scared, and changes throughout the day while you are moving around.

I feel the same. It is mainly because when we are moving fast, the heart beats fast and when we are doing something in a leisure way, it beats slowly. This morning I got up early and went out running on the track field. When my heart beat fast, I stopped running that fast, but slowed my running speed. This is it.

You're making it work harder when you do any form of exercise.

Another way to increase heartbeat is by caffeinated drinks. I use an android app where it can count the number of beats per minute by placing my index finger in front of the phone's camera. If I drink coke, my heart rate increase by 12 beats over normal.

It's simply because the more you do, the more oxygen you need to survive and so the faster your heart pumps the blood around your body to get the oxygen to where it's needed. Your heart could save itself the bother, and you the worry, of changing speed all the time by pumping fast all the time just in case the energy was needed, but then it wouldn't last for very long before stopping and you'd die. So when you are relaxed and not needing too much oxygen and energy in your body, your heart slows down to have a rest.