Your heart is a muscle, about the size of your own fist. It sits in the middle of your chest, tucked a little to the left. All day and all night, your heart squeezes and relaxes to push blood everywhere in your body.

Blood is like a delivery truck. It carries oxygen and food to every part of you, from your brain to your toes. When your heart beats, it sends that blood truck out on its route so all your parts get what they need.

When you run, jump, or play tag, your muscles need more oxygen. So your heart beats faster to deliver blood quicker. That is why your chest thumps and you breathe hard after chasing a friend.

Here is the cool part: your heart is a muscle, so exercise makes it stronger, just like lifting makes your arm muscles stronger. A strong heart can pump more blood with each beat, so it does its job easily.

You do not need a gym to give your heart a workout. Dancing, biking, swimming, or playing outside all count. Doctors say kids should move and play for about sixty minutes every day.

When you rest, put two fingers on your neck or wrist and feel the little thumps. That is your pulse, and each thump is one heartbeat. After you run around, feel it again and notice how much faster it goes.