Patent ductus arteriosus is a common lesion occurring in approximately 10% of infants, about the same incidence as ASD. In the fetus a widely opened, patent vessel connects the pulmonary trunk to the descending aorta. This patent vessel is called a patent ductus arteriosus, (see Fig. 2). Thus, the output of deoxygenated blood from the right ventricle bypasses the unexpanded lungs of the fetus. Blood is propelled form the right ventricle into the pulmonary trunk and through the patent ductus and enters the descending aorta where it is carried to the fetal organ of oxygenation, the placenta abnormality. In the preterm infant the patent ductus may cause minor problems, but if other serious congen¬ital malformations coexist the shunting of blood through the ductus provides a unique mechanism that can be lifesaving.
A. Clinical Features
In the term infant with a patent ductus oxygenated blood flows from the aorta backward into the pulmonary trunk, because the blood pressure and aorta is several times higher than that in the pulmonary circulation. This shunting of blood is called a left-to-right shunt that is similar to that described above with VSDs and ASDs. Left-to-right shunts are noncyanotic congenital heart lesions that are usually well tolerated by the body and give rise to problems only when they are very large shunts or other lesions coexist.

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