Patent ductus arteriosus (PDA) is a heart condition in which a blood vessel that normally closes shortly after birth stays open instead. In a healthy full-term baby, this vessel, called the ductus arteriosus, shuts on its own within the first 48 to 96 hours of life. When it doesn’t close, blood that should flow to the body leaks back into the lungs, forcing the heart to work harder than it should.
What the Ductus Arteriosus Does Before Birth
Before a baby is born, the lungs aren’t doing any breathing. The placenta handles oxygen delivery instead, so there’s no reason to send much blood to the lungs. The ductus arteriosus is a short vessel connecting the pulmonary artery (which leads to the lungs) to the aorta (which carries blood to the rest of the body). It acts as a bypass, routing most blood away from the lungs and straight into circulation. This is completely normal and necessary during fetal development.
At birth, everything changes. The umbilical cord is clamped, the baby takes its first breaths, and the lungs expand. Blood pressure rises throughout the body while pressure in the lungs drops significantly. These pressure shifts eliminate the need for the bypass, and the ductus arteriosus constricts and seals itself. In about 90% of full-term babies, it’s functionally closed within 48 hours. Nearly all have a closed ductus by 96 hours.
Why It Sometimes Stays Open
PDA is the most common cardiovascular condition in premature infants, and the earlier a baby is born, the more likely it is. More than 50% of infants born before 26 weeks of gestation still have an open ductus beyond two months after birth. Their bodies simply haven’t matured enough to trigger the closure process reliably. In full-term infants, PDA is much rarer, occurring in roughly 1 in 2,000 births and accounting for 5% to 10% of all congenital heart disease.
Several factors raise the risk beyond prematurity. Babies born at high altitude (above about 8,200 feet) are more likely to develop PDA, because lower oxygen levels at elevation may interfere with the closure signal. A family history of congenital heart conditions increases risk, as does Down syndrome. Maternal rubella (German measles) during pregnancy can also cause changes in the developing heart that lead to PDA.
Interestingly, some PDAs go undetected for years. Longitudinal studies suggest that “silent” PDAs, those found incidentally on heart imaging without any symptoms, may occur in as many as 1 in 20 births.
How Blood Flow Changes With PDA
Once a baby is born and lung pressure drops, blood pressure in the aorta is higher than in the pulmonary artery. If the ductus stays open, blood flows backward through it, from the aorta into the pulmonary artery and back to the lungs. This is called a left-to-right shunt.
The result is that the lungs receive more blood than they should, and the left side of the heart has to pump a larger volume with each beat to compensate. A small PDA may cause only a trivial amount of extra flow and never produce symptoms. A large PDA floods the lungs with blood, stretches the left side of the heart, and over time can cause the heart to enlarge. If left uncorrected for years, the constant excess pressure in the lung vessels can become permanent, eventually reversing the shunt so that oxygen-poor blood flows into the body. This irreversible stage is called Eisenmenger syndrome, and it’s one of the most serious complications of a large, untreated PDA.
Signs and Symptoms
A small PDA often causes no noticeable symptoms at all. The most common clue is a heart murmur, a whooshing sound a doctor hears through a stethoscope. In older children, the classic PDA murmur has been described as sounding like a washing machine: a continuous rumble that persists through the entire heartbeat cycle. In premature infants, the murmur tends to be less distinct and harder to identify.
When a PDA is large enough to affect blood flow significantly, other signs appear. Babies may breathe rapidly or with visible effort, especially premature infants whose lungs are already immature. Some have difficulty feeding, gain weight slowly, or seem to tire easily. A characteristic physical finding is bounding pulses, meaning the pulse in the arms or legs feels unusually strong and snappy because of the wide swings in blood pressure that a large shunt creates.
How PDA Is Diagnosed
A heart murmur often triggers the initial suspicion, but the definitive diagnosis comes from an echocardiogram, an ultrasound of the heart. This imaging can directly visualize the open ductus and show the direction and volume of abnormal blood flow using color Doppler, which maps moving blood in real time.
Doctors look at several measurements to determine how significant the PDA is. The physical diameter of the ductus matters: an opening of 1.5 mm or larger is a commonly used threshold. They also compare the size of the left atrium to the aorta. When the left atrium is 1.5 times or more the size of the aorta, it signals that the heart is handling a significant volume overload. These measurements together help classify the PDA as small, moderate, or large, which guides treatment decisions.
Treatment With Medication
In premature infants, the first approach to closing a PDA is often medication. These drugs work by blocking the production of chemicals that keep the ductus relaxed and open, essentially nudging the vessel to constrict the way it was supposed to at birth.
Two anti-inflammatory medications and one pain reliever are used for this purpose, and they perform similarly. Clinical trials show no meaningful difference in closure rates between them. What does make a difference is dosing and delivery. Higher doses roughly double the success rate compared to standard doses, with one large analysis finding that high-dose treatment cut the failure rate by about 63%. Oral delivery also tends to outperform intravenous delivery, reducing failure rates by roughly 62% in comparison studies. These medications work best when given in the first days of life, before the ductus has been open long enough to become less responsive.
Catheter and Surgical Closure
When medications don’t work, or when PDA is diagnosed in an older child or adult, the ductus can be closed through a procedure. The two options are catheter-based closure and surgical ligation.
Catheter-based closure is the less invasive approach. A thin tube is threaded through a blood vessel in the leg up to the heart, and a small plug or coil is placed inside the open ductus to block flow. This technique has become increasingly successful even in very small infants. Recent data show a 96% technical success rate in preterm babies weighing 1.5 kg (about 3.3 pounds) or less, and newer devices have allowed the procedure in infants as small as 700 grams (roughly 1.5 pounds).
Surgical ligation involves a small incision in the left side of the chest to tie off or cut the ductus directly. It’s typically reserved for situations where catheter closure isn’t feasible, whether because of the baby’s size, the shape of the ductus, or the level of breathing support the infant requires. The choice between catheter and surgical approaches depends on the individual patient, and practices vary between hospitals.
Outlook After Closure
For the vast majority of children, a closed PDA means the problem is solved permanently. Once the abnormal blood flow stops, the heart gradually returns to its normal size, lung pressures normalize, and no further treatment is needed. Children who have a PDA closed in infancy or early childhood typically have a normal life expectancy with no lasting restrictions on activity.
The picture is different for PDAs that go undetected into adulthood or are left open long enough to cause permanent changes in lung blood vessels. At that point, the damage to the pulmonary arteries may not be reversible, even if the ductus is subsequently closed. This is why identification in infancy, even of PDAs that aren’t causing obvious symptoms, matters for long-term heart health.