The patent ductus arteriosus continues to pose a considerable challenge to clinicians and scientists alike. Why does it close spontaneously in most infants but remain open in others? How best can we select those infants who are most likely to benefit from treatment, i.e. are there echocardiographic criteria that would help in defining a more selective treatment approach? Would it be better to take an aggressive approach and prescribe prophylactic treatment to all extremely immature infants ‑ and if so, what is the best way to define such a subgroup? Or should we be more restrictive in defining treatment indications and adopt a wait and see policy in most, if not all, premature infants? Finally, are there data to suggest that one of the treatment approaches that are available to close the patent ductus arteriosus is superior to the other? This book deals with these questions and tries to give some answers, based on the evidence currently available. It is intended for neonatologists, pediatric cardiologists and researchers.