One of the heart’s main purposes is to keep blood coursing through our bodies, collecting from our lungs the much-needed oxygen it distributes throughout the body. To do this, the one heart has to receive blood simultaneously from two different sources—the lungs and the body—and send it back out in two different directions. The ingeniously designed and deceptively simple structure of the heart makes this feat possible.
In the first step, the heart receives blood in its top two chambers: the atria. The right atrium fills with “used” oxygen-depleted blood from the body, while the left atrium fills with “fresh” oxygen-rich blood from the lungs. With a squeeze, the atria send their individual contents to two larger, muscular ventricles below them. Then, with a second squeeze, the right ventricle sends the “used” blood to the lungs for a fresh load of oxygen, while the left ventricle simultaneously sends its “fresh” blood to the rest of the hungry body.
As marvelous as these muscular chambers may be, they could not do their job without the four one-way valves that open and close at just the right times to keep blood flowing in the right direction. In fact, it is the perfectly timed closing of these valves—in synchronized pairs—that creates the familiar “lub-dub” sound of your heartbeat. “Lub”—two valves below the atria slam shut as the ventricles send blood into the body. “Dub”—those atrial valves reopen while the other pair slam shut so the ventricles can be filled again.
“Lub-dub… lub-dub… lub-dub…” That simple sound emanating from your chest represents an intricately designed dance of muscle, nerve and valve that keeps you alive, every second of every day!