A tiny patch with a big job
Pacemaker cells live in a small patch called the sinoatrial node (SY-no-AY-tree-ul), or SA node. It is in the wall of the top right room of your heart.
These cells are small and pale. They have far fewer squeezing fibers than other heart muscle cells, because their job is making signals, not squeezing.
Try this
Feel your heartbeat! Put two fingers on the side of your neck or the inside of your wrist and count the beats for 15 seconds. Then do 20 jumping jacks and count again.