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Causes

By Mayo Clinic staff

Eisenmenger syndrome develops most often due to a hole between the chambers of your heart. To understand how Eisenmenger syndrome affects your heart and lungs, it's helpful to know how your heart works.

How the heart works
Your heart is divided into four chambers, two on the right and two on the left. In performing its basic job — pumping blood throughout your body — your heart uses its left and right sides for different tasks. The right side moves blood into vessels that lead to your lungs. In your lungs, oxygen enriches your blood, which circulates to your heart's left side. The left side of your heart pumps blood into a large vessel called the aorta, which circulates blood to the rest of your body. Valves control the flow of blood into and out of the chambers of your heart. These valves open to allow blood to move to the next chamber or to one of the arteries, and they close to keep blood from flowing backward.

How Eisenmenger syndrome develops
For most people who have Eisenmenger syndrome, the cause of their condition is due to a hole (shunt) between the main blood vessels or chambers of your heart. This shunt is a heart defect you're born with (congenital). Heart defects that can cause Eisenmenger syndrome include:

• Ventricular septal defect. This shunt in the wall of tissue that divides the right and left sides of your heart's main pumping chambers (ventricles) is the most common cause of Eisenmenger syndrome.
• Atrial septal defect. An atrial septal defect is a shunt in the wall of tissue that divides the right and left sides of the upper chambers of your heart (atria).
• Patent ductus arteriosus. This heart defect is an opening between the pulmonary artery that carries oxygen-poor blood to the lungs and the artery that carries oxygen-rich blood to the rest of your body (aorta).
• Atrioventricular canal defect. In this heart defect, there's a large hole in the center of the heart where the walls between the upper chambers (atria) and lower chambers (ventricles) meet. Some of the valves in your heart also may not function properly.

For each of these defects, the increased pressure of blood flowing through the shunt increases the pressure in your pulmonary artery. Over time, this increased pressure damages the smaller blood vessels in your lungs. The damaged blood vessel walls make it difficult for the red blood cells to take up oxygen. Eisenmenger syndrome occurs when blood flows backward through the shunt, causing oxygen-rich and oxygen-poor blood to mix. This lowers the oxygen level in your blood (cyanosis), and your red blood cell count increases to try and make up for the lack of oxygen.

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