Patent ductus aeriosus. The presence of a murmur could be indicative of any of the conditions. The presence of a continuous machine-like murmur is indicative of a patent ductus aeriosus (PDA). Usually, as in this case, the premature baby with PDA does not acutely become cyanotic and ill, although brief desaturations can occur that become more persistent. An atrial septal defect (ASD), such as a persistent foramen ovale, could be eliminated from the diagnosis because the murmur would be heard as an abnormal splitting of the second sound during expiration (answer a). A patent foramen ovale is a common echo finding in premature babies and is usually not followed up unless it appears remarkable to the pediatric cardiologist or there is a persistent murmur. A patent foramen ovale might result in only minimal or intermittent cyanosis during crying or straining to pass stool. A murmur caused by a ventricular septal defect (VSD, answer c), occurs between the first and second hea sounds (S1and S2) and is described as holosystolic (pansystolic) because the amplitude is high throughout systole. Pulmonary stenosis would be heard as a harsh systolic ejection murmur (answer d). PDA refers to the maintenance of the ductus aeriosus, a normal fetal structure. In the fetus, the ductus aeriosus allows blood to bypass the pulmonary circulation, since the lungs are not involved in CO2/O2exchange until after bih. The placenta subserves the function of gas exchange during fetal development. The ductus aeriosus shunts flow from the left pulmonary aery to the aoa. High oxygen levels after bih and the absence of prostaglandins from the placenta cause the ductus aeriosus to close in most cases within 24 hours. A PDA most often corrects itself within several months of bih, but may require infusion of indomethacin (a prostaglandin inhibitor) as a treatment, inseion of surgical plugs during catheterization, or actual surgical ligation.