It's Great to Circulate
The movement of the blood through the heart and around the body is called circulation (say: sir-kyoo-lay-shun), and your heart is really good at it. It's so good at it that it only takes about 20 seconds to pump blood to every cell in your body. That's less time than you need to sing Take Me Out to the Ballgame! Your body needs this steady supply of blood to keep it working right. It also needs the blood to get rid of waste that would make your body sick if it stuck around.

The left side of your heart sends blood to the body. This blood has lots of oxygen in it, and the oxygen is one of the things that your cells need to stay alive. The body takes the oxygen out of the blood and uses it in your body's cells. The cells say thanks by using the oxygen, making carbon dioxide and other stuff it needs to get rid of, and dumping the carbon dioxide and wastes back into the blood to be carried away. The blood has done the first part of its job by delivering the oxygen to the cells, and now it's time for it to pick up the trash (the carbon dioxide and other waste).

Each time the blood circulates from the heart out to the body, about 20% (one fifth) of it goes through the kidneys where some of the waste is taken out, and then the blood heads back to the heart. The right side of the heart is ready for the hand off: It takes the blood to the lungs for a little freshening up. The carbon dioxide leaves the blood by getting breathed out by the lungs, and the oxygen gets into the blood from the air we breathed in. Now the blood has got the oxygen it needs to go back to the left side of the heart and start all over. And remember, it all happens in less than half a minute!

Blood Gets Around
The heart needs helpers to make sure the blood moves all over, so it works with blood vessels. The heart is attached to these blood vessels, which are like pipes that carry the blood around the body. The blood vessels that carry blood away from the heart (the fresh blood that's full of oxygen) are called arteries, and the ones that carry blood back to the heart are called veins. There are many veins and arteries all throughout your body.

Listen to the Lub-Dub
When you go for a checkup, your doctor uses a stethoscope to listen carefully to your heart. A healthy heart makes a lub-dub sound with each beat. This sound comes from the valves opening and shutting on the blood inside the heart. The first sound (the lub) happens when the blood hits the mitral and tricuspid valves between the atria and ventricles. The next sound (the dub) happens when the blood hits the aortic and pulmonic valves that close up after the blood has been squeezed out of the heart and as the heart relaxes to fill with blood for the next beat. Next time you go to the doctor, ask if you can listen to the lub-dub, too.

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Jump to another section of this article All About the Heart It's Great to Circulate, Blood Gets Around, and Listen to the Lub-Dub Pretty Cool - It's My Pulse! and Keep Your Heart Happy Reviewer name and date on last page