There are four different types of valvular regurgitation, which correspond to the four types of heart valves: aortic regurgitation, mitral regurgitation, tricuspid regurgitation and pulmonary regurgitation.

Aortic regurgitation is a condition in which the aortic valve does not close tightly. Because the defective aortic valve is located between the left ventricle and the aorta, this abnormality allows blood to leak back into the left ventricle instead of going into the aorta and out to the rest of the body. As a result, the body receives less oxygen-rich blood and the left ventricle is stretched (dilated) from the extra blood that pours back into it. Furthermore, the pulse tends to be faster and the systolic blood pressure in the aorta tends to be higher.

There are two forms of aortic regurgitation: acute and chronic. Acute aortic regurgitation is often a medical emergency. Pumping function, blood flow and blood pressure may be suddenly and significantly lessened, usually due to infective endocarditis. It can also be caused by aortic dissection, blunt trauma and surgical errors. Patients with this condition frequently go into shock because the left ventricle cannot rapidly adjust to the sudden rise in blood pressure. Treatment is usually an emergency aortic valve replacement.

Chronic aortic regurgitation develops over a period of years (with or without symptoms). Although the heart initially adapts well to the condition, it may eventually lead to heart failure due to the long period of time during which the ventricles were overworked. Chronic aortic regurgitation is due to scarring from past diseases such as rheumatic fever (now rare in the United States) or endocarditis (an inflammation of the heart lining most often caused by a bacterial infection). The scarring left by these conditions on the heart can affect the function and form of the valves. 

Other conditions that can contribute to the development of chronic aortic regurgitation include:

Mitral regurgitation, which affects about two percent of the U.S. population, is a condition in which the mitral valve, located between the left atrium and the left ventricle, is defective. As a result, the defective mitral valve allows blood to leak back into the left atrium instead of continuing forward into the left ventricle. The extra blood pours back into the left atrium and can lead to lung congestion. The condition can persist for years without detection, as the heart overworks to compensate for the valvular shortcomings. Eventually, overall cardiac efficiency is reduced. Untreated, the left ventricle muscle can eventually thicken until it fails altogether (heart failure).

Mitral regurgitation can be caused by:

• Mitral valve prolapse. This is a condition in which the leaflets of the mitral valve do not close properly. It is the most common cause of mitral valve regurgitation. The condition is sometimes also caused degenerative or myxomatous mitral valve disease.
  
  
• Myxomatous degeneration of the mitral leaflets. A weakening of valve tissue resulting in a loss of tissue elasticity and strength.
  
  
• Dilated, failing left ventricle in which the papillary muscles and chordae supporting the mitral valve fail to allow the valve to close properly.
  
  
• Repeated episodes of cardiac ischemia (in which the heart does not get enough oxygen-rich blood).
  
  
• Scarring due to rheumatic fever or endocarditis.
  
  
• Rupture of the chordae fastening the valve to the chamber wall, sometimes caused by trauma.
  
  
• Congential heart defects.

Tricuspid regurgitation is a condition in which the tricuspid valve (located between the right atrium and the right ventricle) does not close properly. As a result, blood leaks back into the right atrium. A small degree of tricuspid regurgitation occurs in a majority of healthy adults and is not a concern. However, more serious tricuspid regurgitation can be caused by underlying conditions, such as heart failure, lung disorders such as pulmonary embolism or pulmonary hypertension, and thyroid disorders. It can also be caused by valvular abnormalities, such as those caused by prolapse, injury from a pacemaker, endocarditis and rheumatic fever.

Only about 10 percent of the cases of patients with endocarditis involve the tricuspid valve, but this number increases to 50 percent among people who also use intravenous drugs. Because the right ventricle tolerates tricuspid insufficiency relatively well, treatment is aimed at that underlying disease.

Pulmonary regurgitation is a condition in which the pulmonic valve (located between the right ventricle and the pulmonary artery does not close properly. As a result, blood leaks back into the right ventricle instead of traveling through the pulmonary artery to the lungs. Depending on how severe this condition is, as well as its cause (e.g., Congenital heart defects that lead to high pulmonary artery pressures), signs such as cyanosis (a bluish tint to the skin) could result from not enough blood getting to the lungs to absorb oxygen.