Truncus arteriosus (TRUNG-kus ahr-teer-e-O-sus) is a rare heart problem present at birth. That means it's a congenital heart defect. In this condition, one large blood vessel leads out of the heart, instead of two.

Having only one large blood vessel means that oxygen-poor and oxygen-rich blood mix. This mixing reduces the amount of oxygen delivered to the body. It usually increases the amount of blood flow into the lungs too. The heart has to work harder to adjust for the changes in blood flow.

A person with truncus arteriosus also usually has a hole between the two lower heart chambers, called the ventricles. The hole is called a ventricular septal defect.

Another name for truncus arteriosus is common arterial trunk.

Truncus arteriosus is a life-threatening condition. A baby with the condition needs surgery to repair the heart problems and fix blood flow. Surgery is generally successful, especially if done before the baby is 1 month old.


Symptoms of truncus arteriosus usually occur in the first few days of life. They include:

  • Blue or gray skin due to low oxygen levels.
  • Excessive sleepiness.
  • Poor feeding.
  • Poor growth.
  • Pounding heartbeat.
  • Fast breathing.
  • Shortness of breath.

When to see a doctor

If you have concerns about your baby's feedings, sleep patterns or growth, contact your health care provider for an appointment.

Always seek emergency medical care if a baby has any of the following:

  • Blue or gray skin.
  • Fast breathing.
  • Shallow breathing.
  • Any breathing trouble.


Truncus arteriosus occurs as a baby's heart forms during pregnancy. There's often no clear cause. Genetics and environmental factors may play a role.

How the heart works

To understand more about truncus arteriosus, it may be helpful to know how the heart typically works.

The typical heart is made of four chambers. They are:

  • The right upper chamber, also called the right atrium. This heart chamber receives oxygen-poor blood from the body.
  • The right lower chamber, also called the right ventricle. This heart chamber pumps blood into the lungs through a large vessel called the pulmonary artery. The blood flows through the pulmonary artery into smaller vessels in the lungs where blood picks up oxygen.
  • The left upper chamber, also called the left atrium. This heart chamber receives oxygen-rich blood from the lungs through vessels called pulmonary veins.
  • The left lower chamber, also called the left ventricle. This chamber pumps the oxygen-rich blood to the body through the body's largest blood vessel, called the aorta.

A baby's heart before birth

The formation of a baby's heart is complex. At a certain point, babies in the womb have a single large blood vessel exiting the heart. The vessel is called the truncus arteriosus. It usually splits in two as the baby grows in the womb. One part becomes the lower end of the body's main artery, called the aorta. The other part becomes the lower part of the pulmonary artery.

But in some babies, the truncus arteriosus never splits. The wall separating the two lower heart chambers isn't closed completely. This results in a large hole between those chambers, called a ventricular septal defect.

Babies with truncus arteriosus also typically have a problem with the heart valve that controls blood flow from the lower heart chambers to the single vessel. This valve may not close completely when the heart relaxes. Blood can move the wrong way, back into the heart. This is called truncal valve regurgitation.

Risk factors

The exact cause of truncus arteriosus is unknown. But some things might increase the risk of a heart problem at birth. Risk factors include:

  • Viral illness during pregnancy. Some infections can hurt a developing baby. For example, having German measles during pregnancy can cause problems in a baby's heart development. German measles also is called rubella.
  • Poorly controlled diabetes during pregnancy. Careful control of your blood sugar before and during pregnancy can reduce the risk of heart problems in your baby. If you have diabetes, work with your provider to be sure blood sugar is well controlled before getting pregnant.
  • Certain medicines taken during pregnancy. Some medicines can cause heart problems and other health conditions in a baby. Tell your provider about all the medicines you take, including those bought without a prescription.
  • Certain chromosomal disorders. An extra or irregular chromosome increases the risk of truncus arteriosus. Examples are DiGeorge syndrome, also called 22q11.2 deletion syndrome, and velocardiofacial syndrome.
  • Smoking during pregnancy. If you smoke, quit. Smoking during pregnancy increases the risk of heart problems in your baby.
  • Alcohol use. Drinking alcohol during pregnancy increases the risk of heart problems and other health conditions in a baby.
  • Obesity. Obesity increases the risk of giving birth to a baby with a heart problem.


Truncus arteriosus causes severe problems with how blood flows through the lungs, heart and rest of the body.

Complications of truncus arteriosus in babies include:

  • Breathing problems. Extra fluid and blood into the lungs can make it difficult to breathe.
  • High blood pressure in the lungs, also called pulmonary hypertension. This condition causes the blood vessels in the lungs to narrow. It becomes hard for the heart to pump blood into the lungs.
  • Enlargement of the heart. Pulmonary hypertension and increased blood flow strain the heart. The heart must work harder to pump blood. This causes the heart muscle to grow larger. The enlarged heart gradually weakens.
  • Heart failure. In this condition, the heart cannot supply the body with enough blood. Too little oxygen and too much strain on the heart can lead to heart failure.

Even with successful surgical repair of the heart during infancy, other complications can occur later in life. These complications include:

  • Pulmonary hypertension that gets worse.
  • Backward flow of blood through a heart valve, called regurgitation.
  • Heart rhythm problems, also called arrhythmias.

Common symptoms of these complications include:

  • Dizziness.
  • Feeling of rapid, fluttering heartbeats.
  • Feeling very tired.
  • Shortness of breath when exercising.
  • Swelling of the belly, legs or feet.

Truncus arteriosus in adults

Rarely, some people born with truncus arteriosus can survive without surgery to fix the heart problems. They may live into adulthood. But those with the condition will almost certainly have heart failure and develop a complication called Eisenmenger syndrome. This syndrome is caused by permanent lung vessel damage. It results in a significant lack of blood flow to the lungs.


Because the cause is unclear, it may not be possible to prevent truncus arteriosus. Getting good prenatal care is important. If you have a family history of heart problems present at birth, consider talking with a genetic counselor and a heart doctor, called a cardiologist, before getting pregnant.

If you decide to get pregnant, taking these steps can help keep your baby healthy:

  • Get recommended vaccinations. Some infections can be harmful to a developing baby. For example, having German measles — also called rubella —during pregnancy can cause problems in a baby's heart development. A blood test done before pregnancy can determine if you're immune to rubella. A vaccine is available for those who aren't immune.
  • Talk to your provider about your medicines. Check with your health care provider before taking any medicines if you're pregnant or thinking about becoming pregnant. Many drugs aren't recommended for use during pregnancy because they can harm a developing baby.
  • Take a folic acid supplement. Take a multivitamin with folic acid. Taking 400 micrograms of folic acid daily has been shown to reduce brain and spinal cord problems in babies. It may help reduce the risk of heart problems present at birth too.
  • Control diabetes. If you have diabetes, ask your health care provider how to best manage the disease during pregnancy.

Nov. 12, 2022

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