Patent Ductus Arteriosus: How does it work?

By  ,  National Institute of Health
Jan 06, 2013

The Heart With Patent Ductus Arteriosus

The ductus arteriosus is a blood vessel that connects a baby's aorta and pulmonary artery while the baby is in the womb. This connection allows blood to be pumped from the right side of the heart straight to the aorta, without stopping at the lungs for oxygen.

While a baby is in the womb, only a small amount of his or her blood needs to go to the lungs. This is because the baby gets oxygen from the mother's bloodstream.


After birth, the baby is no longer connected to the mother's bloodstream. The baby's blood must now go to his or her own lungs to get oxygen. Normally, as the baby begins to breathe on his or her own, the pulmonary artery opens to allow blood into the lungs, and the ductus arteriosus closes.


Once the ductus arteriosus closes, blood leaving the right side of the heart no longer goes straight to the aorta. First, it goes through the left and right pulmonary arteries and through the lungs to pick up oxygen. Then, the oxygen-rich blood returns to the left side of the heart and is pumped out to the rest of the body.


If the ductus arteriosus doesn't close after birth as it should, it's called a patent ductus arteriosus (PDA). A PDA allows blood to flow directly from the aorta into the pulmonary artery and to the lungs. This extra amount of blood flowing into the lungs strains the heart and increases blood pressure in the lung's arteries.

Effects of Patent Ductus Arteriosus

Full-term infants


A small PDA might not cause any problems, but a large PDA likely will cause problems. The larger a PDA is, the greater the amount of extra blood that passes through the lungs.

A large PDA that remains open for an extended time can cause the heart to enlarge, forcing it to work harder. Also, fluid can build up in the lungs.

A PDA can slightly increase the risk of infective endocarditis (IE). IE is an infection of the lining of the heart, valves, or arteries.

In the case of PDA, the increased flow of blood can irritate the lining of the pulmonary artery where the ductus arteriosus connects. This irritation makes it easier for bacteria in the bloodstream to collect and grow there, which can lead to IE.

Premature infants


PDA can be more serious in premature babies than in full-term babies.

Premature infants who have PDA are more likely to have damage to their lungs from the extra blood flowing through the PDA. These infants may need to be on ventilators to help them breathe.

The increased flow of blood through the lungs also can reduce blood flow to the rest of the body. This can damage other organs, especially the intestines and kidneys.



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