If you’ve ever heard a heartbeat through a stethoscope, you may have heard a “lub-dub, lub-dub” sound as the blood circulates throughout your body. You might wonder how your heart actually works, what that sound means and why we need our blood to circulate.

Your Blood Gets Around

Proper blood circulation is critical to the healthy function of your body. Your heart pumps blood throughout your body to your lungs, muscles and other organs. Blood contains nutrients to feed your cells, and it also carries oxygen to your tissues. Oxygen is important for the production of ATP, a molecule that supplies cells with energy. Your blood picks up oxygen from the lungs as it passes through them. Finally, your blood also helps to remove waste from your body. As the blood circulates around your body, it picks up carbon dioxide—that you’ll get rid of when you exhale—and other waste products that your kidneys will filter before they exit your body.

Your Heart Was Built for This

The four chambers of the heart—two atria (singular is “atrium”) and two ventricles. The smaller atria are the pumps that help fill the larger ventricles. The right atrium and right ventricle pump blood through the lungs to bring oxygen back to the heart. Then the left atrium and ventricle pump this oxygen-rich blood out to the rest of the body, supplying the tissues with oxygen for energy production.

The heart chambers have valves that open and close. The valves build up pressure so the heart can pump blood with force through the body. When these valves open and close, they make sounds—the “lub-dub” you hear. In fact, health care providers can sometimes hear defects in the heart valves simply by listening to differences in that sound.

Show your circulatory system some love during American Heart Month—and all year long. Your heart and blood vessels like healthy food and exercise to stay strong and happy. And if you listen closely enough, you might even hear your heart say “I lub-dub you” back!