How Does It Work?
The heart is located under the rib cage, to the left of the
breastbone (sternum) and between the lungs. Your heart is an amazing
organ. Shaped like an upside-down pear, this fist-sized powerhouse pumps
five or six quarts of blood each minute to all parts of your body. Outside the Heart
Looking at the outside of the heart, you can see the heart is made of muscle. The strong muscular walls contract (squeeze), pumping blood to the arteries.The major blood vessels that enter the heart include:
- aorta
- superior vena cava
- inferior vena cava
- pulmonary artery takes oxygen-poor blood from the heart to the lungs
- pulmonary vein -- brings oxygen-rich blood from the lungs to the heart
- the coronary arteries.
Inside the heart
The heart is a four-chambered, hollow organ.It is divided into the left and right side by a muscular wall called the septum. The right and left sides of the heart are further divided into:
- two atria - top chambers, which receive blood from the veins and
- two ventricles - bottom chambers, which pump blood into the arteries
The normal aortic valve
- mitral valve
- tricuspid valve
- aortic valve
- pulmonic valve (also called pulmonary valve)
The heart valves work the same way as one-way valves in the plumbing of your home, preventing blood from flowing in the wrong direction.
Each valve has a set of flaps, called leaflets or cusps. The mitral valve has two leaflets; the others have three. The leaflets are attached to and supported by a ring of tough, fibrous tissue called the annulus. The annulus helps to maintain the proper shape of the valve.
The leaflets of the mitral and tricuspid valve are also supported by tough, fibrous strings called chordae tendineae. These are similar to the strings supporting a parachute. The chordae tendineae extend from the valve leaflets to small muscles, called papillary muscles, which are part of the inside walls of the ventricles
The atria and ventricles work together, alternately contracting and relaxing to pump blood through your heart. The electrical system of your heart is the power source that makes this possible.
The heart's electrical system
Your heartbeat is triggered by electrical impulses that travel down a special pathway through your heart:
- SA node (sinoatrial node) – known as the heart’s natural pacemaker
The impulse starts in a small bundle of specialized cells located in the right atrium, called the SA node. The electrical activity spreads through the walls of the atria and causes them to contract. This forces blood into the ventricles.
The SA node sets the rate and rhythm of your heartbeat. Normal heart rhythm is often called normal sinus rhythm because the SA (sinus) node fires regularly. - AV node (atrioventricular node)
The AV node is a cluster of cells in the center of the heart between the atria and ventricles, and acts like a gate that slows the electrical signal before it enters the ventricles. This delay gives the atria time to contract before the ventricles do. - His-Purkinje Network
This pathway of fibers sends the impulse to the muscular walls of the ventricles and causes them to contract. This forces blood out of the heart to the lungs and body. - The SA node fires another impulse and the cycle begins again.
How fast does the normal heart beat?
How fast the heart beats depends on the body's need for oxygen-rich blood. At rest, the SA node causes your heart to beat about 50 to 100 times each minute. During activity or excitement, your body needs more oxygen-rich blood; the heart rate rises to well over 100 beats per minute.Medications and some medical conditions may affect how fast your heart-rate is at rest and with exercise.
How do you know how fast your heart is beating?
You can tell how fast your heart is beating (your heart rate) by feeling your pulse. Your heart-rate is the amount of times your heart beats in one minute.You will need a watch with a second hand.
You should feel a tapping or pulsing against your fingers.
Count the number of taps you feel in 10 seconds.
Multiply that number by 6 to find out your heart-rate for one minute:
Pulse in 10 seconds x 6 = ____ beats per minute (your heart-rate)
When feeling your pulse, you can also tell if your heart rhythm is regular or not.
The right and left sides of the heart work together
Right Side
Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium.Left Side
The pulmonary vein empties oxygen-rich blood, from the lungs into the left atrium.Atrial contraction
Right Side
Blood flows from your right atrium into your right ventricle through the open tricuspid valve. When the ventricles are full, the tricuspid valve shuts. This prevents blood from flowing backward into the atria while the ventricles contract (squeeze).Left Side
Blood flows from your left atrium into your left ventricle through the open mitral valve. When the ventricles are full, the mitral valve shuts. This prevents blood from flowing backward into the atria while the ventricles contract (squeeze).Ventricular contraction
Oxygen and carbon dioxide travels to and from tiny air sacs in the lungs, through the walls of the capillaries, into the blood.
Right Side
Blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs.Left Side
Blood leaves the heart through the aortic valve, into the aorta and to the body. This pattern is repeated, causing blood to flow continuously to the heart, lungs and body.How does blood flow through your lungs?
Once blood travels through the pulmonic valve, it enters your lungs. This is called the pulmonary circulation. From your pulmonic valve, blood travels to the pulmonary artery to tiny capillary vessels in the lungs. Here, oxygen travels from the tiny air sacs in the lungs, through the walls of the capillaries, into the blood. At the same time, carbon dioxide, a waste product of metabolism, passes from the blood into the air sacs. Carbon dioxide leaves the body when you exhale. Once the blood is purified and oxygenated, it travels back to the left atrium through the pulmonary veins.The heart receives its own supply of blood from the coronary arteries. Two major coronary arteries branch off from the aorta near the point where the aorta and the left ventricle meet. These arteries and their branches supply all parts of the heart muscle with blood.
Right Coronary Artery (RCA)
The right coronary artery branches into:
- Right marginal artery
- Posterior descending artery
The right coronary artery supplies:
- right atrium
- right ventricle
- bottom portion of both ventricles and back of the septum
Left Main Coronary Artery (also called the left main trunk)
The left main coronary artery branches into:
- Circumflex artery
- Left Anterior Descending artery (LAD)
The left coronary arteries supply:
- Circumflex artery - supplies blood to the left atrium, side and back of the left ventricle
- Left Anterior Descending artery (LAD) - supplies the front and bottom of the left ventricle and the front of the septum
What is collateral circulation?
Collateral circulation is a network of tiny blood vessels, and, under normal conditions, not open. When the coronary arteries narrow to the point that blood flow to the heart muscle is limited (coronary artery disease), collateral vessels may enlarge and become active. This allows blood to flow around the blocked artery to another artery nearby or to the same artery past the blockage, protecting the heart tissue from injury.- Learn more about coronary artery disease
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There are four valves within your heart. They are the mitral, tricuspid, aortic and pulmonic valve.The mitral valve and tricuspid valve lie between the atria (upper heart chambers) and the ventricles (lower heart chambers). The aortic valve and pulmonic valve lie between the ventricles and the major blood vessels leaving the heart.
As blood leaves each chamber of the heart, it passes through a valve. Your heart valves make sure that blood flows in only one direction through your heart.
A Closer Look at the Valves
Mitral Valve Mouse-over image to see the mitral valve open.
Aortic Valve Mouse-over image to see the aortic valve open.The valve is made of strong, thin pieces or flaps of tissue called leaflets.The leaflets are attached to and supported by a ring of tough fibrous tissue called the annulus. The annulus helps to provide support and maintain the proper shape of the valve.
The valve leaflets can be compared to doors opening and closing. While the annulus functions as the door frame.
The leaflets of the mitral and tricuspid valve are also supported by tough, fibrous strings called chordae tendineae. These are similar to the strings supporting a parachute. The chordae tendineae extend from the valve leaflets to small muscles, called papillary muscles, which are part of the inside walls of the ventricles. The chordae tendineae and papillary muscles keep the leaflets stable against any backward flow of blood.
How Valves Work
The right and left sides of the heart work together to pump blood throughout the whole body. The four heart valves make sure that blood always flows freely in a forward direction and that there is no backward leakage.
1. Blood flows from your right and left atria into your ventricles through the open mitral and tricuspid valves.
2. When the ventricles are full, the mitral and tricuspid valves shut. This prevents blood from flowing backward into the atria while the ventricles contract (squeeze).
3. As the ventricles begin to contract, the pulmonic and aortic valves are forced open and blood is pumped out of the ventricles through the open valves into the pulmonary artery toward the lungs, and the aorta, to the body.
4. When the ventricles finish contracting and begin to relax, the aortic and pulmonic valves snap shut. These valves prevent blood from flowing back into the ventricles.This pattern is repeated, causing blood to flow continuously to the heart, lungs and body. - Learn more about valve disease
- Your system of blood vessels -- arteries, veins and capillaries -- is over 60,000 miles long. That's long enough to go around the world more than twice!
- The adult heart pumps about 5 quarts of blood each minute - approximately 2,000 gallons of blood each day - throughout the body.
- When attempting to locate their heart, most people place their hand on their left chest. Actually, your heart is located in the center of your chest between your lungs. The bottom of the heart is tipped to the left, so you feel more of your heart on your left side of your chest.
- The heart beats about 100,000 times each day.
- In a 70-year lifetime, the average human heart beats more than 2.5 billion times
- An adult woman's heart weighs about 8 ounces, a man's about 10 ounces
- A child's heart is about the size of a clenched fist; an adult's heart is about the size of two fists.
- Blood is about 78 percent water.
- Blood takes about 20 seconds to circulate throughout the entire vascular system.
- The structure of the heart was first described in 1706, by Raymond de Viessens, a French anatomy professor.
- The electrocardiograph (ECG) was invented in 1902 by Dutch physiologist Willem Einthoven. This test is still used to evaluate the heart's rate and rhythm.
- The first heart specialists emerged after World War I.
Resources
Topol EJ (ed). Cleveland Clinic Heart Book (2000) New York: Hyperion.Topol EJ (ed). Textbook of Cardiovascular Medicine (1998), Philadelphia: Lippincott-Raven.
The Heart and Blood Vessels
Large red vessel- the aorta;large artery that carries blood from of the left ventricle to the arteries of the body
Large blue vessel- vena cava;
(includes the superior and inferior vena cava);
large vein that empties blood into the right atrium of the heart.
Right Coronary Artery (RCA) - supplies blood to the right atrium, right ventricle, bottom portion of the left ventricle and the back of the septum
Left Coronary Artery (LCA) - divides into two branches: the circumflex artery & the left anterior descending artery
Left anterior descending artery (LAD) - supplies blood to the front and bottom of the left ventricle and the front of the septum
Coronary veins (in blue) -take oxygen-poor ("deoxygenated") blood that has already been "used" by muscles of the heart and returns it to the right atrium
Circumflex artery - supplies blood to the left atrium and the side and back of the left ventricle
Pulmonary veins - bring oxygen-rich blood back to the heart from the lungs
As the heart beats, it pumps blood through a system of blood vessels,
called the circulatory system. The vessels are elastic tubes that carry
blood to every part of the body.
Blood flows continuously through your body's blood vessels. Your heart is the pump that makes it all possible.
The aorta is the large artery leaving the heart. The superior vena cava is the large vein that brings blood from the head and arms to the heart, and the inferior vena cava brings blood from the abdomen and legs into the heart.
Veins (in blue) are the blood vessels that return blood to the heart.
Deep veins, located in the center of the leg near the leg bones, are enclosed by muscle. The iliac, femoral, popliteal and tibial (calf) veins are the deep veins in the legs.
Superficial veins are located near the surface of the skin and have very little muscle support. The great saphenous vein is a superficial vein.
Blood is essential
- It carries oxygen and nutrients to your body's tissues
- It takes carbon dioxide and waste products away from the tissues.
- It is needed to sustain life and promote the health of all the body's tissues.
There are three main types of blood vessels
Arteries
The arteries (red) carry oxygen and nutrients away from your heart, to your body's tissues.
The veins (blue) take oxygen-poor blood back to the heart.
The veins (blue) take oxygen-poor blood back to the heart.
- Arteries begin with the aorta, the large artery leaving the heart.
- They carry oxygen-rich blood away from the heart to all of the body's tissues.
- They branch several times, becoming smaller and smaller as they carry blood further from the heart.
Capillaries
- Capillaries are small, thin blood vessels that connect the arteries and the veins.
- Their thin walls allow oxygen, nutrients, carbon dioxide and waste products to pass to and from the tissue cells.
Veins
- These are blood vessels that take oxygen-poor blood back to the heart.
- Veins become larger and larger as they get closer to the heart.
- The superior vena cava is the large vein that brings blood from the head and arms to the heart, and the inferior vena cava brings blood from the abdomen and legs into the heart.
Blood flows continuously through your body's blood vessels. Your heart is the pump that makes it all possible.
Upper Body Circulation
In the lungs, the pulmonary arteries (in blue) carry unoxygenated blood from the heart into the lungs. Throughout the body, the arteries (in red) deliver oxygenated blood and nutrients to all of the body’s tissues, and the veins (in blue) return oxygen-poor blood back to the heart.The aorta is the large artery leaving the heart. The superior vena cava is the large vein that brings blood from the head and arms to the heart, and the inferior vena cava brings blood from the abdomen and legs into the heart.
Lower Body Circulation
Arteries (in red) are the blood vessels that deliver blood to the body.Veins (in blue) are the blood vessels that return blood to the heart.
Deep veins, located in the center of the leg near the leg bones, are enclosed by muscle. The iliac, femoral, popliteal and tibial (calf) veins are the deep veins in the legs.
Superficial veins are located near the surface of the skin and have very little muscle support. The great saphenous vein is a superficial vein.
Educational Opportunities
Additional Secure Online Services include:
- MyChart - a secure online tool connecting patients to their own health information from the privacy of their home - clevelandclinic.org/mychart
- MyConsult Online Medical Second Opinion - a secure online service providing remote medical second opinions. Learn more at clevelandclinic.org/myconsult
Cleveland Clinic offers a variety of learning opportunities for health care professionals.
Live and Online Presentations
- Grand Rounds and Conferences - Plan to attend a lively CME-approved presentation related to advancements in the diagnosis and treatment of cardiovascular disease. (Access our calendar).
- OnLine CME - FREE CME credit. Heart and vascular topics, and more.
- Physicians can manage their CME credits by using the myCME Web Portal. Available 24/7, the site offers CME opportunities to medical professionals across the globe.
- Presentations - Non-CME presentations from our Heart and Vascular Institute physicians on our website
Journals, Books and Resources
- Cardiac Consult - Free newsletter for physicians, available online and by subscription.
- Cleveland Clinic Journal of Medicine - Published twelve times yearly by Cleveland Clinic, available online and by subscription.
- Disease Management Project - An online medical resource authored by physicians from Cleveland Clinic.
- Books - Textbooks & information for medical professionals from leading authorities.
- Physician eNewsletter - Have the latest cardiovascular health information delivered to your inbox.
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