Patent ductus arteriosus (PDA) occurs when a blood vessel that is normal while a baby in the womb fails to close after the baby is born. The cause of the problem is not known and it affects one in 2000 babies that are born each year. It is more common in girls and much more common in premature infants. It may occur in children with otherwise normal hearts and occurs commonly in association with complex heart defects such as hypoplastic left heart syndrome, transposition of the great arteries

Pulmonary atresia (PA) is a complicated congenital (present at birth) defect that occurs when the pulmonary valve, located between the right ventricle and pulmonary artery, is not formed properly.

Pulmonary stenosis is relatively common and accounts for about 10% of heart defects diagnosed during childhood. It can occur in children with otherwise normal hearts or along with other congenital heart defects such as atrial septal defect or Tetralogy of Fallot. It occurs more frequently in children with Noonan syndrome and Williams syndrome which are both rare genetic conditions.