As a baby develops in the womb, a vascular connection (ductus arteriosus) between two major blood vessels leading from the heart — the aorta and pulmonary artery — is a normal and necessary part of your baby's blood circulation while in the womb. The ductus arteriosus diverts blood from the lungs of the fetus while they aren't being used. The fetus receives oxygen from the mother's circulation. But, the ductus arteriosus is supposed to close within two or three days after birth once the newborn's heart adapts to life outside the womb. In premature infants, the connection often takes longer to close on its own. If the connection remains open, it's referred to as a patent ductus arteriosus.

The abnormal opening causes too much blood to circulate to the lungs and heart. If not treated, the blood pressure in the lungs may increase (pulmonary hypertension) and the heart may enlarge and weaken.

Congenital heart defects arise from problems early in the heart's development — but there's often no clear cause. Genetics and environmental factors may play a role.

Dec. 22, 2011

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