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patent ductus arteriosus, PDA
Patent ductus arteriosus, or PDA, is a malformation of the heart caused by failure of normal closure of the ductus arteriosus, a direct connection between the aorta and the pulmonary artery which is present and functional during fetal life but which is unnecessary once air-breathing begins. Normally the ductus closes shortly after birth; this process of closure by muscular contraction is reversible for a short time - it can be reopened under hormonal control (prostaglandins). However, within a few weeks it is permanently closed.
If the ductus fails to close normally, a loud to-and-fro murmur will result (the so-called "machinery murmur"). Very young patients with heart or lung disease may need to have the ductus repaired to prevent too much blood from flowing back from the high pressure side of the circulation - the aorta. This lesion also places an older patient at some risk of bacterial endocarditis, so ordinarily the patent ductus is surgically tied off.