patent ductus arteriosus (PDA), an abnormal opening between the pulmonary artery and the aorta caused by failure of the fetal ductus arteriosus to close after birth. It is seen primarily in premature infants. The defect allows blood from the aorta to flow into the pulmonary artery and recirculate through the lungs, where it is reoxygenated and returned to the left atrium and left ventricle, placing an increased workload on the left side of the heart and causing increased pulmonary vascular congestion and resistance. Clinical manifestations include cardiomegaly, especially of the left atrium and left ventricle; dilated ascending aorta; bounding pulses resulting from increased systolic pressure; tachycardia; and a typical machinery-like murmur that is heard during all of systole and most of diastole. Characteristic auscultatory and radiological findings are sufficient to confirm diagnosis so that cardiac catheterization is not necessary. Correction is delayed until the child is old enough to tolerate surgery and until spontaneous closure, which sometimes occurs. Untreated complications include congestive heart failure, pulmonary vascular disease, calcification of the ductal site, and infective endocarditis. See also congenital cardiac anomaly.
