biologic control of the duct Krichenko A, Benson LN, Burrows P, et al Angiographic classification of the isolated, persistently patent ductus arteriosus and implications for percutaneous catheter occlusion Am J Cardiol 1989;63:877–880 Interested in a categorization scheme for ductal geometry, these authors proposed an easy classification that allows retrospective data analysis Smallhorn JF, Huhta JC, Anderson RH, Macartney FJ Suprasternal cross-sectional echocardiography in assessment of patent ductus arteriosus Br Heart J 1982;48:321–330 The first study defining the technique for imaging the duct by two-dimensional echocardiography Lloyd TR, Beekman RH III Clinically silent patent ductus arteriosus Am Heart J 1994;127:1664– 1665 Salazar J, Olivan P, Ibarra F, et al Silent uncomplicated patent ductus arteriosus in children Diagnosis with echo-doppler [Spanish] Servicio de Espanola De Cardiologia 1990;43:410–412 Houston AB, Gnanapragasam JP, Lim MK, Doig WB, Coleman E Doppler ultrasound and the silent ductus arteriosus Br Heart J 1991;65:97– 99 Balzer DT, Spray TL, McMufflin D, Cottingham W, Canter CE Endarteritis associated with a clinically silent patent ductus arteriosus Am Heart J 1993;125:1192–1193 Parthenakis FI, Kanakaraki MK, Vardas PE Images in cardioogy: silent patent ductus arteriosus endarteritis Heart 2000;84:619 Malnick SD, Shimoni S, Zimhony O An unusual case of endocarditis Cal Med Assoc J 2006;174:1087–1088 These articles established the existence of the socalled silent (nonhypertensive) duct, and the specter of its potential risk for endarteritis Campbell M Natural history of persistent ductus arteriosus Br Heart J 1968;30:4–13 Campbell analyzed four series of patients in which 11 examples of spontaneous closure occurred over 1842 patient-years, giving a rate of 0.6% per annum However, several of the examples were based on quite tenuous clinical impressions In none was catheterization performed before and after the event The figure calculated by Campbell is almost certainly an overestimate He did not suggest that surgery should be delayed except, perhaps, in patients with small shunts and signs that the duct was already closing Few cardiologists would now agree even with these exceptions Jacobs JP, Giroud JM, Quintessenza JA, et al The modern approach to patent ductus arteriosus treatment: complementary roles of videoassisted thoracoscopic surgery and interventional cardiology coil occlusion Ann Thorac Surg 2003;76:1421–1427 An excellent review of the application of thorascopic surgery and percutaneous coil embolization Both techniques are complementary, and a rationale for selection of the appropriate treatment modality can be based on the size and age of the patient and the size and morphology of the duct Portsmann W, Wierny L, Warnke H Closure of persistent ductus arteriosus without thoracotomy Ger Med Month 1967;12:259–261 Rashkind WJ, Cuaso CC Transcatheter closure of a patent ductus arteriosus: successful use in a 3.5-kg infant Pediatr Cardiol 1979;1:3–7 Cambier PA, Kirby WC, Wortham DC, Moore JW Percutaneous closure of the small (