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How does your heart work? Get the details

Reviewed 3/27/2023

Anatomy of the heart

Your heart is the engine that drives your body. Without it, blood couldn't circulate and your organs wouldn't get the oxygen and nutrients they need to work properly.

The heart is found behind the rib cage in the center of the chest between the lungs. A normal and healthy adult heart is about the size of a fist.

Learn more about the structures that make the heart's continuous pumping cycle possible.


The heart gets the oxygen it needs through the coronary arteries—blood vessels that start at the top of the heart and spread across the heart's surface.


This large vein is the passageway for deoxygenated (oxygen-poor) blood returning to the heart from the head, chest and arms. The superior vena cava empties into the heart's upper-right chamber, the right atrium.


This large vein enters the heart's upper right chamber, the right atrium, from underneath. It carries deoxygenated blood back to the heart from the legs, pelvis and abdomen.


This chamber receives the deoxygenated blood returning from the body. It also holds the sinoatrial node, which sends out the electrical signals that start each heartbeat. The deoxygenated blood flows from the right atrium down into the right ventricle, to the lungs and on to the rest of the heart's valves and chambers.


Blood enters the right ventricle from the right atrium above it. The right ventricle then pumps the blood out into the pulmonary artery, which leads to the lungs.


This artery carries blood out of the heart's lower right chamber, the right ventricle. The artery divides into two branches that lead to the lungs. The blood flows into tiny blood vessels in the lungs, releases waste products gathered from throughout the body and absorbs fresh oxygen.


This upper-left heart chamber receives oxygen-rich blood fresh from the lungs. It then squeezes the blood down into the left ventricle.


This chamber is the last stop for oxygen-rich blood on its way out of the heart. It also is the strongest chamber, with thicker muscular walls than the right ventricle. It uses this strength to propel blood through the aortic valve into the aorta, the main artery for blood traveling from the heart out into the body.


The aorta is about as big around as a garden hose, making it the largest artery in the entire body. This is the passageway for oxygen- and nutrient-rich blood to leave the heart's left ventricle and start the journey to every organ, tissue and cell.


This wall of tissue separates the heart's two sides.


The pericardium is a two-layered sac of tissue that envelops the heart. These two thin layers of tissue hold the heart in place as it beats and help protect it from being harmed by chest infections. The two layers are separated by lubricating fluid that prevents them from rubbing against each other and causing friction.


The myocardium, also called the heart muscle, is the heart's center layer and provides the power that pushes blood through the heart's four chambers.


The innermost layer of the heart's walls lines the inner heart chambers and each of the heart's valves.


Nestled in the wall of the right atrium, this bundle of tissue sends out precisely timed electrical signals that set the heart's pace. These signals travel through each of the heart's chambers, causing each to contract in carefully timed succession. The contractions squeeze blood along its path through the heart's valves and chambers.

You can think of the sinoatrial node as the heart's pacemaker.


This valve sits between the right atrium and right ventricle-the upper and lower chambers of the heart's right side. It's the first valve that deoxygenated blood passes through after returning to the heart from the far reaches of the body.


This valve sits between the right ventricle and the pulmonary artery. Contractions of the right ventricle send deoxygenated blood through this valve and on its way to the lungs for a fresh supply of oxygen.


The mitral valve sits between the upper and lower chambers on the heart's left side. It opens and closes to allow a one-way flow of blood from the left atrium down into the left ventricle.


This valve sits between the left ventricle and the body's largest artery-the aorta. Oxygen-rich blood leaves the heart through this valve and travels into the aorta on its way to the rest of the body.



Sources: American Heart Association; Merck Manuals Online Medical Library; National Cancer Institute; National Heart, Lung, and Blood Institute; Society for Vascular Surgery

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