A heart murmur is heard when blood passes through an opening that makes it turbulent. Could be caused by defective valves (stenotic or prolapse/insufficient), holes that should be closed (atrial/ventricle septums), or unusual connections (patent ductus arteriosis). It is not uncommon for newborns to have a patent ductus arteriosis (embryonic connection between aortic arch and pulmonary artery)--this could cause a murmur but is usually beningn and will close on its own or with indomethacin. Newborn could have patent foramen ovale (between left and right atria)--this is also usually benign. Other causes of heart murmurs in newborns: 1. Ventricular septal defect 2. congenital bicuspid aortic valve 3. tetralogy of fallot (pulmonic stenosis, overiding aorta, ventricular septal defect, right ventricular hypertrophy) many many others......I can t remember without digging up books/notes.