There are four valves that control the flow of blood through the four chambers of the heart (listed below in the same order as blood flows through the heart):

• Tricuspid valve (in the right side of the heart between the right atrium and right ventricle)
• Pulmonic valve (in the right side of the heart between the right ventricle and the pulmonary artery)
• Mitral valve (in the left side of the heart between the left atrium and left ventricle - and the only valve with 2 leaflets instead of 3)
• Aortic valve (in the left side of the heart between the left ventricle and the aorta)

The Tricuspid and Mitral valves open during diastole, which is the period of time when the ventricles are filling with blood. The Pulmonic and Aortic valves open during systole when blood is being ejected from the heart.

Disease can affect these valves in two ways.

• Stenosis is a narrowing of the valve so that blood cannot move through as freely as necessary.
• Regurgitation is a failure of the one-way valve so that blood flows back through the valve in the wrong direction.

The valves most commonly affected by disease are the mitral valve, which controls flow of the blood from the left upper chamber, or atrium, to the left lower chamber, and the aortic valve, which controls blood flow out of the left ventricle to the rest of the body.

Purpose of the Four Heart Valves

The purpose of the valves in the heart is very simple: they make sure that blood flows only in one direction. That is, they make sure that when the heart squeezes, blood flows in the proper direction and not backwards. When the heart squeezes and relaxes with each heart beat, the squeezing only raises and lowers the pressure inside the heart. How the blood moves under those changes in pressure is determined by how well the valves work and how easily blood can flow into and out of the heart.

There are four valves in the heart, corresponding to the four chambers in the heart:

• The tricuspid valve divides the right atrium from the right ventricle. The right atrium receives blood returning from the body through the superior and inferior vena cavae, and pushes that blood into the right ventricle. The right atrium is a low-pressure pump, and serves mainly to push a little extra blood with each heartbeat into the more powerful right ventricle.
• The pulmonic valve divides the right ventricle from the pulmonary artery. The right ventricle receives blood from the right atrium and pushes it into the pulmonary arteries, whence it goes to the lungs to soak up oxygen.
• The mitral valve divides the left atrium from the left ventricle. The left atrium receives oxygenated blood from the lungs and pushes it into the left ventricle. The left atrium is a low-pressure pump, and serves as a reservoir and to a lesser extent to push blood into the left ventricle.
• The aortic valve separates the left ventricle from the aorta. The left ventricle receives blood from the left atrium and pushes it into the aorta. The left ventricle generates the blood pressure that pushes blood through the body.

Blood Flow Through the Heart

The circulation is driven by the movement of blood generated by the events of the cardiac cycle.

1. The right atrium receives deoxygenated blood from the body tissues
2. The right ventricle then pumps the blood into the pulmonary artery
3. Oxygenated blood returns to the pulmonary veins.
4. The left ventricle then pumps a volume of blood into the aorta.

The system of blood vessels that carries blood to the lungs and back is called the pulmonary circulation. All other blood vessels in the body are collectively known as the systemic circulation. The atrioventricular valves (the tricuspid and mitral valves) prevent backflow of blood during ventricular contraction (systole). The aortic and pulmonic valves open during systole, then close during diastole to prevent backflow of blood. In the following sequence, the heart fills with blood, excitation of the cardiac muscle occurs and the ventricles contract to expel a single stroke volume into the circulation.

Step 1 Blood comes into the heart through two large veins; one from the upper part of the body and one from the lower part. The first chamber it enters in the right side of the heart is the right atrium.	Step 2 Then it crosses the tricuspid valve (the valve between the right atrium and right ventricle) and flows into the right ventricle. Right and left are reversed in these pictures because we are looking at the front of the heart.	Step 3 The right ventricle contracts and pressure increases to the point where the pulmonic valve opens.	Step 4 From the right ventricle, the blood is pumped into the lungs via the pulmonary arteries. These are the only arteries in the body that carry deoxygenated blood.
Step 5 The pulmonary arteries continue to branch and become smaller in diameter as they infiltrate the lung tissue, eventually forming a capillary network around an alveolus.	Step 6 The alveolus is an air sac that communicates with the outside to allow carbon dioxide to be removed from the blood and oxygen to enter across a thin tissue membrane.	Step 7 Once oxygenated blood has returned to the left side of the heart from the lungs, the left ventricle contracts and pumps the oxygen-rich blood to peripheral organs.	Step 8 Inside an organ, the blood vessel has a different structure and is called an arteriole. The arterioles infiltrate most organs, eventually forming a capillary network

Obviously, any defect or problem with a heart valve can impair the blood flow through the heart, and even out to the system.

Clinical Presentation

SYMPTOMS
Common symptoms of valvular heart disease may include the following:

• Weakness on exertion
• Rapid heartbeat
• Chest discomfort
• Fainting spells
• No symptoms at all in some patients

Valvular heart disease is commonly caused by damage to the heart muscle as a result of rheumatic fever or a congenital abnormality. In older persons, the heart valves can become calcified as part of the aging process, thus become narrowed and stiff, or in some cases, incompetent so that they leak blood back into the atria. Valvular heart problems can be corrected surgically, by direct repair of the valve, replacement of the damaged valve with an artificial valve, or by a nonsurgical technique called balloon valvuloplasty. Patients with valvular heart disease are also at risk for bacterial endocarditis.

HEART MURMURS
A heart murmur is an abnormal sound in the heart. Generally, during a routine office visit, the doctor listens to the heart using a stethoscope and can detect a murmur if present. In most cases, heart murmurs do not affect the person's health and result in some form of irregular blood flow through the heart. Some, however, are due to underlying defects in the heart or its valves and may require treatment.

Valvular defects refer to abnormalities of the valves that keep blood from flowing "backwards" into the heart chambers. A defective valve may allow blood to back up in the wrong direction or it may block the passage of blood, thereby interrupting the normal flow. Most heart murmurs require no special treatment other than leading a healthy lifestyle in general -- not smoking, reducing stress, eating wisely and exercising regularly. Valvular defects can sometimes be treated medically; however, if the valve is severely diseased or defective, surgery may be recommended to replace the damaged valve(s).

Cardiac auscultation remains the most widely used method of screening for heart disease. The production of murmurs is due to 3 main factors: (1) high blood flow rate through normal or abnormal orifices; (2) forward flow through a narrowed or irregular orifice into a dilated vessel or chamber; or (3) backward or regurgitant flow through an incompetent valve, septal defect, or patent ductus arteriosus.

A heart murmur may have no pathological significance or may be an important clue to the presence of valvular, congenital, or other structural abnormalities of the heart (8). Most systolic heart murmurs do not signify cardiac disease, and many are related to physiological increases in blood flow velocity. In other instances, a heart murmur may be an important clue to the diagnosis of undetected cardiac disease (eg, valvular aortic stenosis) that may be important even when asymptomatic or that may define the reason for cardiac symptoms. In these situations, various noninvasive or invasive cardiac tests may be necessary to establish a firm diagnosis and form the basis for rational treatment of an underlying disorder. Two-dimensional (2-D) and Doppler echocardiography is particularly useful in this regard.

An important consideration in a patient with a cardiac murmur is the presence or absence of symptoms. For example, symptoms of syncope (passing out), angina pectoris (chest discomfort), or congestive heart failure in a patient with a midsystolic murmur will usually result in a more aggressive approach than in patients with a similar midsystolic murmur who have none of these symptoms. 2-D and Doppler echocardiography to rule in or out the presence of significant aortic stenosis will likely be obtained. A history of thromboembolism or possible infective endocarditis will also usually result in a more extensive workup. In patients with cardiac murmurs and clinical findings suggestive of endocarditis, 2-D and Doppler echocardiography is usually indicated.

Specific Valvular Disorders

AORTIC REGURGITATION
Aortic regurgitation is a condition in which the aortic valve allow blood to flow back into the left ventricle from the aorta. Some of the blood that should be flowing to the body from the heart instead flows back into the left ventricle as soon as the heart stops squeezing. As a result, the left ventricle has to pump more blood than normal in order to deliver the normal blood flow to the body. Acute aortic regurgitation is a medical emergency that requires in-hospital treatment under the care of one or more specialists. Most patients have chronic aortic regurgitation.

Chronic aortic regurgitation can be caused by a number of diseases, such as chronic hypertension that dilates the aortic root, rheumatic valvular disease, chest trauma, infection of the heart valve (endocarditis), certain congenital disorders, and autoimmune diseases. If this condition is mild, there is a minimal effect on overall health. If the condition is moderate or severe, however, the left ventricle must enlarge in order to maintain its high pumping volume or cardiac output. If the enlargement process goes too far, permanent damage can occur and replacement of the valve can become dangerous.

People with chronic aortic regurgitation can do well for many years when they follow a low salt diet and take drug therapy that controls the symptoms of congestive heart failure and helps reduce the amount of blood that flows back into the heart after each heart beat (afterload reducing agents). It is important to replace the valve before irreversible damage to the left ventricle occurs, however.

AORTIC STENOSIS
Aortic stenosis is a condition in which the aortic valve is stiff and the aperture is narrowed. This means that the opening through which blood must flow is too small, so that the left ventricle must generate higher pressure in order to maintain normal blood flow. When the condition is mild, there are usually no discernible ill effects. When the condition is severe, however, it can be life-threatening.

The aortic valve can become stenotic in three situations:

• Bicuspid aortic valve (up to 2% of infants are born with two instead of three leaflets in their aortic valves)
• Rheumatic valvular disease
• Age-related calcification of the previously normal aortic valve.

The first two circumstances are more common in people younger than 65 years, while the last is more common in older people.

The aortic valve is usually replaced if aortic stenosis causes angina pectoris, syncope (fainting), or congestive heart failure. People who suffer these symptoms because of aortic stenosis often die within two to five years, sometimes suddenly. The stenotic aortic valve can be replaced safely in almost all patients who are otherwise healthy. Decreased left ventricular function, which can prevent surgery in other conditions, is not a reason to avoid surgery in aortic stenosis. This is true because the left ventricle is straining against a tight valve, and almost always recovers when the tight valve is replaced with an artificial one.

Replacement of the stenotic aortic valve is sometimes recommended in patients who have not yet developed symptoms but who have very narrow valves (e.g., valve area less than or equal to 0.7 square centimeters). Not all physicians agree on when to do valve replacement surgery in people with aortic stenosis who have no symptoms. The rationale for doing so it that the first symptom of aortic stenosis can be sudden death.

MITRAL REGURGITATION
Mitral regurgitation is a condition in which the mitral valve allows blood to flow back from the left ventricle into the left atrium during systolic contraction. The left ventricle generates the highest pressure of any of the four chambers in the heart, while the left atrium normally experiences only normal pressures.

Acute mitral regurgitation is a medical emergency that requires in-hospital treatment under the care of one or more specialists. Chronic mitral regurgitation is far more common. The mitral valve can become regurgitant for many reasons, including:

• Age-related degeneration
• Rheumatic valvular disease
• Previous infection of the valve (endocarditis)
• Chest trauma
• Left ventricular enlargement due to previous myocardial infarction or some other cause

If chronic mitral regurgitation is mild, there is a minimal effect on the overall health of the person (except for the need for prophylactic antibiotics). Many patients who have left ventricular enlargement from causes such as damage to heart muscle from heart attacks will have mild to moderate mitral regurgitation.

If the condition is moderate to severe, the left atrium will enlarge ("dilate") to compensate for the extra volume it faces: not only must it hold the blood returning from the lungs between heart beats, but it must also hold the extra blood that leaks backward when the left ventricle contracts. The left ventricle also, over time, can enlarge because it too must handle the extra volume of blood that returns from the left atrium. Enlargement of the left atrium can cause several types of symptoms: fatigue, pulmonary edema, atrial fibrillation and atrial flutter, and left atrial thrombi (clots) that can cause strokes. Enlargement of the left ventricle can cause both forward and backward congestive heart failure, either of which can be fatal.

MITRAL STENOSIS
Mitral stenosis is a condition in which the mitral valve is narrowed and/or non-compliant, so that blood cannot flow easily from the left atrium to the left ventricle. In response, the left atrium will enlarge ("dilate") to develop the extra pressure it needs to push blood into the left atrium. The pressure in the left atrium rises above normal, leading to shortness of breath. This happens because the blood from the lungs drains into the left atrium. Like a stopped-up toilet, the amount of blood in the blood vessels of the lungs increases if flow into the left atrium is slowed by increased left atrial pressure. This extra blood in the lungs then leaks into the air spaces of the lungs, causing shortness of breath. Often, the symptom of shortness of breath (dyspnea") is worsened by exertion or by lying down for several hours (e.g., at night during sleep).

The enlargement can, and often does, lead to atrial fibrillation, which can lead to stroke. If mitral Stenosis is mild, there is a minimal effect on the overall health of the person (except for the need for prophylactic antibiotics). If the condition is moderate to severe, the person develops symptoms that can be difficult to control, including dyspnea, swelling of the legs and abdomen, and even syncope and chest pain. Dangerous problems with thrombus formation in the left atrium can lead to stroke, heart attack, or infarction in other parts of the body such as the arm, kidney, or spleen.

MITRAL VALVE PROLAPSE
Mitral valve prolapse is a relatively common disorder, and affects from 2 to 10 percent of the general population, depending on the study. A more recent study of a large population in Massachusetts suggest that mitral valve prolapse is not as common as we once thought and that the previous high percentage was a false positive due to the type of echocardiogram that was being performed. Although it usually causes no trouble at all, it is associated with bothersome symptoms in some people and serious problems in about one in ten persons with the disorder.

TRICUSPID REGURGITATION
Tricuspid regurgitation is a condition in which the tricuspid valve is too leaky, so that blood flows backward from the right ventricle to the right atrium. It occurs in two settings: by itself, and in combination with a disease process that elevates right ventricular pressure. It is relatively uncommon.

TRICUSPID STENOSIS
Tricuspid stenosis is a condition in which the tricuspid valve is too tight. This is almost always due to rheumatic valvular disease, and is usually associated with rheumatic damage to the mitral and/or the aortic valves.

PULMONIC REGURGITATION
Pulmonic regurgitation is a condition in which the pulmonic valve allows blood to flow back into the right ventricle from the pulmonary artery. It is quite rare. In the unusual case of severe pulmonic regurgitation associated with right heart failure, despite administration of digoxin, valve replacement should be considered.

PULMONIC STENOSIS
Pulmonic stenosis is a condition in which the pulmonic valve is narrow. It is also relatively rare. In severe cases, correction of the stenosis can often be accomplished with balloon valvuloplasty. If that is not possible, surgical valvulotomy without valve replacement usually suffices. Replacement of the stenotic pulmonic valve is rare.

Artificial Valves

Replacement of diseased natural heart valves with artificial ones has been life saving. However, as in so much of medicine today, the replacements valves are never as good as natural, healthy valves. Prosthetic (artificial) heart valves have been used for the past several decades.

The manufacture of prosthetic heart valves has been studied so intensively that valves are considered successful when they have performed well for 20 years and more. There are two general types of valves: mechanical and bioprosthetic (usually taken from pigs). The mechanical valves last longer but require the person to take blood thinners (anticoagulants).

• The Starr-Edwards valve has a caged-ball design and has performed well since 1965.
• The Bjork-Shiley, has a tilting-disk design, and has been in use since about 1970
• The newer St. Jude, and Medtronic-Hall valves also have a tilting-disk design. Of the tilting-disk designs, the St. Jude appears to have the most favorable properties especially in children and small adults.

The bioprosthetic valves do not require long-term anticoagulation, but frequently must be replaced after only about 10 years or so in adults. They are often selected by women who wish to become pregnant and by elderly people. They often need to replaced much more quickly in children and in people with diseased kidney function who are on hemodialysis.

The major risk of prosthetic heart valves is stroke, which can occur in several each year out of each 100 people who have certain artificial valves. The reason seems to be that, despite considerable engineering research and development, the flow of blood across the prosthetic valve is turbulent, not smooth. This leads to formation of blood clots ("thrombi", technically, since they form inside the body), which can float into the brain. When they reach the brain, they float into smaller and smaller arteries until they reach arteries that are thinner than they are. They plug up these arteries, which prevents oxygen from reaching the part of the brain supplied by those arteries, which in turn causes a stroke. In general, the risk of stroke is higher for mitral valve replacement than for aortic valve replacement, perhaps because blood flows more slowly across the mitral valve and therefore has more time to form thrombi.

Anticoagulation

Anticoagulation is the process of preventing blood from clotting. When blood clots outside the body, it is called a "blood clot." When the same thing happens inside the body, it is called a "thrombus."

The body has its own natural anticoagulation mechanism. A person should consider using artificial anticoagulation when he or she has enough of an increased risk of forming a thrombus to justify the risks of artificial anticoagulation. Some of the circumstances that make long-term artificial anticoagulation attractive are: having certain types of prosthetic heart valves, having atrial fibrillation, and recurrent stroke, pulmonary embolism or deep vein thrombosis in the legs. Reasons for short-term (3 to 6 months) anticoagulation include first episodes pulmonary embolism or deep vein thrombosis, documented left ventricular thrombus following acute myocardial infarction.

TYPES OF ANTICOAGULATION
There are three methods of anticoagulation: oral, subcutaneous, and intravenous. The oral method uses a medicine called warfarin. The subcutaneous and intravenous methods use the naturally occurring substance heparin. The subcutaneous method, in which medicine is injected under the skin, uses either unmodified heparin or the newer forms of heparin called "low-molecular weight heparin." The intravenous method, in which medicine is injected directly into the blood stream via a vein, uses unmodified heparin.

Warfarin is taken once a day. Its dose must be adjusted daily, based on the result of a blood test called the "Prothrombin time", until the blood test result is satisfactory day after day. Then, it is tested weekly, and finally monthly (as a practical matter). The reason for testing is that the dose required for safe and effective anticoagulation varies from person to person. Moreover, it varies in the same person from week to week depending on the diet. Because warfarin acts by opposing the body's ability to use Vitamin K to the proteins it needs for normal coagulation, the dose of warfarin changes if a person eats more or less Vitamin K than he or she usually does.

THE NATURAL ANTICOAGULATION MECHANISMS
The body has its own natural anticoagulation mechanism. It is normally balanced very precisely agains the natural coagulation mechanism so that we tend to form clots but not thrombi. When this balance is upset, people form thrombi that can cause considerable damage such as pulmonary emboli (in the lungs) and strokes (in the brain). People who are at particularly high risk for thrombus formation include those who do not move around much (such as people who have just had surgery on a hip or people who have sat still in a car or airplane for six to 12 hours straight), those who have diseases such as certain types of cancer or certain complex rheumatologic diseases, and those who have deficiencies of or abnormalities in the proteins the body uses in its anticoagulation mechanism (including Protein S, Protein C, Antithrombin III, and Factor V).

Endocarditis

The endocardium is the membrane that covers the inner wall of the heart's four chamber and valves. Bacterial Endocarditis occurs when bacteria lodge in the endocardium and begin to grow. The symptoms of Endocarditis are:

• Fever
• Night sweats, chills, heart murmur,
• Loss of appetite
• Joint pain

People most likely to get bacterial endocarditis include those with a history of:

• Heart surgery
• Rheumatic fever
• Congenital heart malformation
• Artificial heart valve

Even a mild heart condition that causes no symptoms, such as mitral valve prolapse, can place a person at risk for bacterial endocarditis. Such people should be given antibiotics before dental work or surgery, or during a skin or lung infection, all of which increase the risk of endocarditis. People with these risk factors should also know that they increase their risk of getting endocarditis if they are drug users who share needles.

Bacterial endocarditis is a serious disease that is fatal if not treated with antibiotics. Even with treatment, permanent heart damage can result. If you are at risk for bacterial endocarditis, alert your healthcare provider before having surgery or dental work. Your dentist will prescribe antibiotics before and after dental work. Practice daily oral hygiene and get regular dental checkups.