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 - Northwestern Memorial Hospital - Chicago

About the Heart

The heart is the largest muscle in the human body. It is about the size of a closed fist. The average heart beats 100,000 times a day. During this time, it pumps about 2,000 gallons of blood. It pumps blood and needed nutrients to the lungs and to all the body tissues. To do this, the heart's mechanical and electrical systems must work together.


The heart has four chambers. The two upper, thin-walled chambers are the right atrium and left atrium. The two larger, more powerful chambers are the right ventricle and left ventricle.

The right heart chambers receive blood from the body and pump it to the lungs via the pulmonary artery. There it picks up oxygen. The left heart chambers receive this oxygen-rich blood from the lungs by way of the pulmonary vein. Then oxygen-rich blood travels from the heart through the aorta to all parts of the body.

Four "one-way" valves control the flow of blood through the heart. The opening and closing of these valves is what makes the sound of the heart beat. The tricuspid valve is between the right atrium and right ventricle. The mitral valve is located between the left atrium and left ventricle. Two other valves are found just before the aorta and pulmonary artery. These are called the aortic and pulmonic valves.

Oxygen is delivered to the heart itself via coronary arteries which lie on the surface of the heart.

For the heart to do its work it needs a "spark plug" or electrical impulse to "start" a heartbeat. The heart receives this electrical signal from the sinus node in the upper chamber or right atrium. This signal or "spark" starts the electrical activity. The signal then travels through the upper chambers (atria) along a standard path to the lower chambers or ventricles via the atrioventricular node (AV), bundle of His and two thin fibers called the right and left bundle branches. This electrical circuit makes the heart contract and pump blood throughout the body. When the circuit follows this standard path, it is called normal sinus rhythm.


For more information regarding the Bluhm Cardiovascular Institute, please call 1-866-662-8467 or request a first time appointment online.

Last UpdateMarch 18, 2011