Flexi Says: Patent ductus arteriosus (PDA) is a congenital heart defect that is a problem with the heart structure present at birth. There is a persistent opening between the two major blood vessels leading from the heart in the baby with PDA. That opening is actually a normal part of a baby's circulatory system in the womb but gets closed shortly after birth. If the opening fails to close, it's called a patent ductus arteriosus. This opening allows poorly oxygenated blood flow through the heart in an abnormal pattern, which causes weakening of the heart muscle, persistent fast breathing, or breathlessness and may lead to heart failure.