Your heart is a muscular organ that acts like a pump
to send blood throughout your body all the time.
Your heart is at the center of
your circulatory system, which delivers blood to all areas of your body. An
electrical system regulates the heart and uses electrical signals to contract
the hearts walls. When the walls contract, blood is pumped into your
circulatory system.
Your circulatory system is made up of a network of blood
vessels, such as arteries, veins, and capillaries. The vessels in this network
carry blood to and from all areas of your body. A system of inlet and outlet
valves in your hearts chambers works to ensure that blood flows in the
right direction.
Your heart is vital to your health and nearly
everything that goes on in your body. Without the hearts pumping action,
blood cant circulate within your body.
Your blood carries the oxygen and
nutrients that your organs need to function normally. Blood also carries carbon
dioxide, a waste product, to your lungs to be passed out of your body and into
the air. A healthy heart supplies the areas of your body with the right amount
of blood at the right rate needed to function normally. If disease or injury
weakens your heart, your bodys organs wont receive enough blood to
function normally.
Anatomy of the Heart
Your heart is located under the ribcage in the
center of your chest between your right and left lung. Its 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
vesselsarteries and veinsthat 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 its 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
bodys 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
hearts 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 its
pumped out of your hearts left ventricle. Your coronary arteries are
located on your hearts 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
its 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 hearts 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 hearts
left atrium. From the left atrium, the blood is pumped into the left ventricle,
where its pumped to the rest of your body through the aorta.
For the heart to function properly, your blood flows
in only one direction. Your hearts valves make this possible. Both of
your hearts 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
hearts 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.
Heart Contraction and Blood Flow
The animation below shows how your heart pumps blood. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame of the animation. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.
The animation shows how blood flows through the heart as it contracts and relaxes.
Heartbeat
Almost everyone has heard the real or recorded sound of a heartbeat. When your heart beats, it makes a "lub-DUB" sound. Between the time you hear "lub" and "DUB," blood is pumped through your heart and circulatory system.
A heartbeat may seem like a simple event repeated over and over. A heartbeat actually is a complicated series of very precise and coordinated events that take place inside and around your heart. Each side of your heart uses an inlet valve to help move blood between the atrium and ventricle. The tricuspid valve does this between the right atrium and ventricle. The mitral valve does this between the left atrium and ventricle. The "lub" is the sound of the mitral and tricuspid valves closing.
Each of your heart's ventricles has an outlet valve. The right ventricle uses the pulmonary valve to help move blood into the pulmonary arteries. The left ventricle uses the aortic valve to do the same for the aorta. The "DUB" is the sound of the aortic and pulmonary valves closing.
Each heartbeat has two basic parts: diastole (di-AS-toe-lee, or relaxation) and atrial and ventricular systole (SIS-toe-lee, or contraction). During diastole, the atria and ventricles of your heart relax and begin to fill with blood. At the end of diastole, your heart's atria contract (an event called atrial systole) and pump blood into the ventricles. The atria then begin to relax. Next, your heart's ventricles contract (an event called ventricular systole) and pump blood out of your heart.
Pumping Action
Your heart uses the four valves to ensure your blood flows only in one direction. Healthy valves open and close in coordination with the pumping action of your heart's atria and ventricles. Each valve has a set of flaps called leaflets or cusps. These seal or open the valves. This allows pumped blood to pass through the chambers and into your blood vessels without backing up or flowing backward.
Blood without oxygen from the two vena cavae fill your heart's right atrium. The atrium contracts (atrial systole). The tricuspid valve located between the right atrium and ventricle opens for a short time and then shuts. This allows blood to enter into the right ventricle without flowing back into the right atrium.
When your heart's right ventricle fills with blood, it contracts (ventricular systole). The pulmonary valve located between your right ventricle and pulmonary artery opens and closes quickly. This allows blood to enter into your pulmonary artery without flowing back into the right ventricle. This is important because the right ventricle begins to refill with more blood through the tricuspid valve. Blood travels through the pulmonary arteries to your lungs to pick up oxygen.
Oxygen-rich blood returns from the lungs to your heart's left atrium through the pulmonary veins. As your heart's left atrium fills with blood, it contracts. This event also is called atrial systole. The mitral valve located between the left atrium and left ventricle opens and closes quickly. This allows blood to pass from the left atrium into the left ventricle without flowing back into the left atrium.
As the left ventricle fills with blood, it contracts. This event also is called ventricular systole. The aortic valve located between the left ventricle and aorta opens and closes quickly. This allows blood to flow into the aorta. The aorta is the main artery that carries blood from your heart to the rest of your body. The aortic valve closes quickly to prevent blood from flowing back into the left ventricle, which is already filling up with new blood.
Circulation and Blood Vessels
Your heart and blood vessels make up your overall blood circulatory system. Your overall blood circulatory system is made up of four subsystems.
Arterial Circulation
Arterial circulation is that part of your overall blood circulatory system that involves arteries, like the aorta and pulmonary arteries.
Arteries are blood vessels that carry blood away from your heart. Healthy arteries are strong and elastic. They become narrow between beats of the heart, and they help keep your blood pressure consistent. This helps blood circulate efficiently through your body.
Arteries branch into smaller blood vessels called arterioles. Arteries and arterioles have strong, flexible walls that allow them to adjust the amount and rate of blood flowing to different parts of your body.
Venous Circulation
Venous circulation is the part of your overall blood circulatory system that involves veins, like the vena cavae and pulmonary veins. Veins are blood vessels that carry blood to your heart. Veins have thinner walls than arteries. Veins can increase in width as the amount of blood passing through them increases.
Capillary Circulation
Capillary circulation is the part of your circulatory system where oxygen, nutrients, and waste pass between your blood and parts of your body.
Capillaries connect the arterial and venous circulatory subsystems. Capillaries are very small blood vessels.
The importance of capillaries lies in their very thin walls. Unlike arteries and veins, capillary walls are thin enough that oxygen and nutrients in your blood can pass through the walls to the parts of your body that need them to function normally. Capillaries' thin walls also allow waste products like carbon dioxide to pass from your body's organs and tissues into the blood where it's taken away to your lungs.
Pulmonary Circulation
Pulmonary circulation is the movement of blood from the heart to the lungs and back to the heart again. Pulmonary circulation includes both arterial and venous circulation.
Blood without oxygen is pumped to the lungs from the heart (arterial circulation). Oxygen-rich blood moves from the lungs to the heart through the pulmonary veins (venous circulation).
Pulmonary circulation also includes capillary circulation. Oxygen you breathe in from the air passes through your lungs into your blood through the many capillaries in the lungs. Oxygen-rich blood moves through your pulmonary veins to the left side of your heart and out the aorta to the rest of your body. Capillaries in the lungs also remove carbon dioxide from your blood so that your lungs can breathe the carbon dioxide out into the air.
Your Hearts Electrical System
The animation below shows how your heart's electrical system works. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame of the animation. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.
The animation shows how the heart's internal electrical conduction system causes the heart to pump blood.
Your hearts electrical system controls all the
events that occur when your heart pumps blood. The electrical system also is
called the cardiac conduction system. If youve ever seen the heart test
called an
EKG
(electrocardiogram), youve seen a graphical picture of the electrical
activity of your heart.
Your hearts electrical system is made up of
three main parts:
The sinoatrial (SA) node located in the right
atrium of your heart
The atrioventricular (AV) node located on the
interatrial septum close to the tricuspid valve
The His-Purkinje system located along the walls
of your hearts ventricles
A heartbeat is a complicated series of events that
take place in your heart. A heartbeat is a single cycle in which your
hearts chambers relax and contract to pump blood. This cycle includes the
opening and closing of the two inlet and outlet valves of the right and left
ventricles of your heart.
Each heartbeat has two basic parts: diastole, and
atrial and ventricular systole. During diastole, the atria and ventricles of
your heart relax and begin to fill with blood. At the end of diastole, your
hearts atria contract (atrial systole), pumping blood into the
ventricles, and then begin to relax. Your hearts ventricles then contract
(ventricular systole), pumping blood out of your heart.
Each beat of your heart is set in motion by an
electrical signal from within your heart muscle. In a normal, healthy heart,
each beat begins with a signal from the SA node. This is why the SA node is
sometimes called your hearts natural pacemaker. Your pulse, or heart
rate, is the number of signals the SA node produces per minute.
The signal is generated as the two vena cavae fill
your hearts right atrium with blood from other parts of your body. The
signal spreads across the cells of your hearts right and left atria. This
signal causes the atria to contract. This action pushes blood through the open
valves from the atria into both ventricles.
The signal arrives at the AV node near the
ventricles (see red burst on picture), where it slows for an instant to allow
your hearts right and left ventricles to fill with blood. The signal is
released and moves to the His bundle located in the walls of your
hearts ventricles.
From the His bundle, the signal fibers divide into
left and right bundle branches through the Purkinje fibers that connect
directly to the cells in the walls of your hearts left and right
ventricles (see yellow on the picture). As the signal spreads across the cells
of your hearts ventricle walls, both ventricles contract, but not at
exactly the same moment. The left ventricle contracts an instant before the
right ventricle. This pushes blood through the pulmonary valve (for the right
ventricle) to your lungs, and through the aortic valve (for the left ventricle)
to the rest of your body.
As the signal passes, the walls of the ventricles
relax and await the next signal.
This process continues over and over as the atria
refill with blood and other electrical signals come from the SA node.
Heart Disease
Your heart is made up of many parts working together to pump blood. In a healthy heart, all the parts work well so that your heart pumps blood normally. Then all parts of your body that depend on the heart to deliver blood also stay healthy.
Heart disease can disrupt a heart's normal electrical system and pumping functions. Diseases and conditions of the heart's muscle make it difficult for your heart to pump blood normally. Damaged or diseased blood vessels make the heart work harder than normal. Problems with the heart's electrical system, called arrhythmias, can make it difficult for the heart to pump blood efficiently.