Cardiac Center

How the Normal Heart Works

Before you begin reading about particular heart defects, please read the explanation of how the normal heart works for a basic understanding of its structure and function.

The heart is a large muscular organ with the very important job of circulating Normal Heart
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Heart Illustration
blood through the blood vessels to the body. Located in the center of the chest, the heart is the hardest working muscle in the human body — always working, even while we are sleeping. The heart and blood vessels together make up the body's cardiovascular system and are vital to supplying the body with the necessary oxygen and nutrients needed to survive. When you breathe, your lungs take in oxygen. The heart pumps blood to the lungs to pick up oxygen, and then it pumps blood through the body to deliver that oxygen.

The animations below show how a normal heart pumps blood. They also explain the changes that happen to a normal heart right after the fetus is born.


The structure of the heart

The heart is a two-sided pump made up of four chambers: the upper two chambers called atria and the lower two called the ventricles.

Heart valves

There are four valves within the heart. Each valve has flaps that prevent blood from flowing in the wrong direction — opening to allow forward flow of blood and closing to prevent backward flow.

How blood circulates through the heart and body

The four chambers of the heart are attached to major veins or arteries that either bring blood into or carry blood away from the heart.

The heart's control system

A heartbeat is caused by an electrical impulse traveling through the heart. The heart's built-in electrical system controls the speed of its pumping. The electrical impulse originates in the sinus node which functions as the heart's natural pacemaker. The sinus node is most often located in the top of the right atrium. The electrical signals travel through the heart tissue causing the atria and ventricles to contract and relax and the blood to be pumped to the body.

Reviewed by: Marie M. Gleason, MD
Date: May 2013

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