Atrioventricular canal defect can involve only the two upper chambers of the heart (partial) or all four chambers (complete). In either type, extra blood circulates in the lungs.

Complete atrioventricular canal defect

Signs and symptoms usually develop in the first several weeks of life. These signs and symptoms are generally similar to those associated with heart failure and might include:

• Difficulty breathing or rapid breathing
• Wheezing
• Fatigue
• Lack of appetite
• Poor weight gain
• Pale skin color
• Bluish discoloration of the lips and skin
• Excessive sweating
• Irregular or rapid heartbeat
• Swelling in the legs, ankles and feet (edema)

Partial atrioventricular canal defect

Signs and symptoms might not appear until early adulthood and might be related to complications that develop as a result of the defect. These signs and symptoms can include:

• Abnormal heartbeat (arrhythmia)
• Shortness of breath
• High blood pressure in the lungs (pulmonary hypertension)
• Heart valve problems
• Heart failure

Atrioventricular canal defect occurs before birth when a baby's heart is developing. Some factors, such as Down syndrome, might increase the risk of atrioventricular canal defect. But the cause is generally unknown.

The normal-functioning heart

The heart is divided into four chambers, two on the right and two on the left.

The right side of your heart moves blood into vessels that lead to the lungs. There, oxygen enriches the blood. The oxygen-rich blood flows back to your heart's left side and is pumped into a large vessel (aorta) that 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 close to keep blood from flowing backward.

Happens in atrioventricular canal defect

In partial atrioventricular canal defect:

• There's a hole in the wall (septum) that separates the upper chambers (atria) of the heart.
• Often the valve between the upper and lower left chambers (mitral valve) also has a defect that causes it to leak (mitral valve regurgitation).

In complete atrioventricular canal defect:

• There's a large hole in the center of the heart where the walls between the atria and the lower chambers (ventricles) meet. Oxygen-rich and oxygen-poor blood mix through that hole.
• Instead of separate valves on the right and left, there's one large valve between the upper and lower chambers.
• The abnormal valve leaks blood into the ventricles.
• The heart is forced to work harder and enlarges.

Factors that might increase a baby's risk of developing atrioventricular canal defect before birth include:

• Down syndrome
• German measles (rubella) or another viral illness during a mother's early pregnancy
• Alcohol consumption during pregnancy
• Poorly controlled diabetes during pregnancy
• Smoking during pregnancy
• Certain medications taken during pregnancy — talk to your doctor before taking any drugs while you're pregnant or trying to become pregnant
• Having a parent who had a congenital heart defect

Complications of atrioventricular canal defect can include:

• Enlargement of the heart. Increased blood flow through the heart forces it to work harder than normal, causing it to enlarge.
• Pulmonary hypertension. When there is a hole (defect) that allows mixing of oxygenated (red) and deoxygenated (blue) blood, the amount of blood that goes to the lungs is increased. This results in pressure buildup in the lungs, causing high blood pressure in the lungs.
• Respiratory tract infections. Atrioventricular canal defect can cause recurrent bouts of lung infections.
• Heart failure. Untreated, atrioventricular canal defect usually results in the heart's inability to pump enough blood to meet the body's needs.