Your Heart and Blood

Your heart is a muscle about the size of your fist. It pumps blood all around your body, day and night, without ever stopping for a rest. Even while you sleep, your heart keeps right on working — it is the most hard-working muscle you have.

Make a fist and squeeze it tight, then let go. That squeeze-and-release is just like a heartbeat. Each time your heart squeezes, it pushes blood out; each time it relaxes, it fills up again, ready for the next beat. That squeezing is what you feel as your pulse.

Blood carries oxygen and food to every part of your body and takes away waste. It travels through tubes called blood vessels — a network so long it could wrap around the Earth many times! Without this delivery service, your cells would have no fuel to do their jobs.