Anatomy of the Heart

Your heart is located under the ribcage in the center of your chest between your right and left lung. It’s shaped like an upside-down pear. Its muscular walls beat, or contract, pumping blood continuously to all parts of your body.

The size of your heart can vary depending on your age, size, or the condition of your heart. A normal, healthy, adult heart most often is the size of an average clenched adult fist. Some diseases of the heart can cause it to become larger.

The Exterior of the Heart

Below is a picture of the outside of a normal, healthy, human heart.

Heart Exterior

The illustration shows the front surface of the heart, including the coronary arteries and major blood vessels.

The heart is the muscle in the lower half of the picture. The heart has four chambers. The right and left atria (AY-tree-uh) are shown in purple. The right and left ventricles (VEN-trih-kuls) are shown in red.

Connected to the heart are some of the main blood vessels—arteries and veins—that make up your blood circulatory system.

The ventricle on the right side of your heart pumps blood from the heart to your lungs. When you breathe air in, oxygen passes from your lungs through blood vessels where it’s added to your blood. Carbon dioxide, a waste product, is passed from your blood through blood vessels to your lungs and is removed from your body when you breathe air out.

The atrium on the left side of your heart receives oxygen-rich blood from the lungs. The pumping action of your left ventricle sends this oxygen-rich blood through the aorta (a main artery) to the rest of your body.

The Right Side of Your Heart

The superior and inferior vena cavae are in blue to the left of the muscle as you look at the picture. These veins are the largest veins in your body. They carry used (oxygen-poor) blood to the right atrium of your heart. “Used” blood has had its oxygen removed and used by your body’s organs and tissues. The superior vena cava carries used blood from the upper parts of your body, including your head, chest, arms, and neck. The inferior vena cava carries used blood from the lower parts of your body.

The used blood from the vena cavae flows into your heart’s right atrium and then on to the right ventricle. From the right ventricle, the used blood is pumped through the pulmonary (PULL-mun-ary) arteries (in blue in the center of picture) to your lungs. Here, through many small, thin blood vessels called capillaries, your blood picks up oxygen needed by all the areas of your body.

The oxygen-rich blood passes from your lungs back to your heart through the pulmonary veins (in red to the left of the right atrium in the picture).

The Left Side of Your Heart

Oxygen-rich blood from your lungs passes through the pulmonary veins (in red to the right of the left atrium in the picture). It enters the left atrium and is pumped into the left ventricle. From the left ventricle, your blood is pumped to the rest of your body through the aorta.

Like all of your organs, your heart needs blood rich with oxygen. This oxygen is supplied through the coronary arteries as it’s pumped out of your heart’s left ventricle. Your coronary arteries are located on your heart’s surface at the beginning of the aorta. Your coronary arteries (shown in red in the drawing) carry oxygen-rich blood to all parts of your heart.

The Interior of the Heart

Below is a picture of the inside of a normal, healthy, human heart.

Heart Interior

The illustration shows a cross-section of a healthy heart and its inside structures. The blue arrow shows the direction in which low-oxygen blood flows from the body to the lungs. The red arrow shows the direction in which oxygen-rich blood flows from the lungs to the rest of the body.

The Septum

The right and left sides of your heart are divided by an internal wall of tissue called the septum. The area of the septum that divides the two upper chambers (atria) of your heart is called the atrial or interatrial septum. The area of the septum that divides the two lower chambers (ventricles) of your heart is called the ventricular or interventricular septum.

Heart Chambers

The picture shows the inside of your heart and how it’s divided into four chambers. The two upper chambers of your heart are called atria. The atria receive and collect blood. The two lower chambers of your heart are called ventricles. The ventricles pump blood out of your heart into the circulatory system to other parts of your body.

Heart Valves

The picture shows your heart’s four valves. Shown counterclockwise in the picture, the valves include the aortic (ay-OR-tik) valve, the tricuspid (tri-CUSS-pid) valve, the pulmonary valve, and the mitral (MI-trul) valve.

Blood Flow

The arrows in the drawing show the direction that blood flows through your heart. The light blue arrows show that blood enters the right atrium of your heart from the superior and inferior vena cavae. From the right atrium, blood is pumped into the right ventricle. From the right ventricle, blood is pumped to your lungs through the pulmonary arteries.

The light red arrows show the oxygen-rich blood coming in from your lungs through the pulmonary veins into your heart’s left atrium. From the left atrium, the blood is pumped into the left ventricle, where it’s pumped to the rest of your body through the aorta.

For the heart to function properly, your blood flows in only one direction. Your heart’s valves make this possible. Both of your heart’s ventricles has an “in” (inlet) valve from the atria and an “out” (outlet) valve leading to your arteries. Healthy valves open and close in very exact coordination with the pumping action of your heart’s atria and ventricles. Each valve has a set of flaps called leaflets or cusps, which seal or open the valves. This allows pumped blood to pass through the chambers and into your arteries without backing up or flowing backward.