Back Heart Defects Causing Extra Blood Flow Through the Lungs Heart defects that cause too much blood flow through the lungs require clinical care by a physician or other healthcare professional. Listed in the directory below are some of these defects, for which we have provided a brief overview. Patent Ductus Arteriosus (PDA) Atrial Septal Defect (ASD) Ventricular Septal Defect (VSD) Atrioventricular Canal (AV Canal or AVC)