A diagram showing a Patent Ductus Arteriosus (PDA) via Wikipedia
Patent ductus arteriosus is a congenital heart defect that prevents proper blood flow from the heart.
In a fetus in the uterus, blood flow from the pulmonary artery would have too much pressure for the collapsed, unused lungs in the developing fetus. Blood flow at full pressure would damage all the arteries in the developing lung. As such, in a fetus, there is a hole between the pulmonary artery and the aorta called the ductus arteriosus. Instead of all the blood flowing to the unused lungs, most of it is diverted to the aorta where it is distributed to the rapidly growing body.
However, after a newborn draws its first breath, the lungs expand and blood can start flowing into them at full pressure with no ill effects. The ductus arteriosus starts to close and is usually fully sealed within the first few weeks after birth.
Diagram "F" shows a phonocardiogram of a patient with PDA, courtesy MadHero88, via Wikipedia
However, in some individuals, the ductus never closes, generally because prostaglandins in the blood prevent the body from closing the opening. As such, blood pressure to the two main arteries in the body is lessened and deoxygenated blood in the pulmonary artery flows into the aorta, while some oxygenated blood in the aorta flows back into the lungs. This keeps blood pressure low and results in many disorders from oxygen starvation, such as fatigue and fainting.
The disorder is usually detected in childhood, but in rare cases is not detected until the patient reaches adulthood. In either case, the preferred treatment is the same - closing the ductus surgically. However, when surgery is impossible or inadvisable, the use of some non-steroidal anti-inflammatories, such as ibuprofen can block the effect of the prostaglandins and allow the ductus to close naturally. This was the approach taken in Body and Soul.
Patent ductus arteriosus at NIH