This podcast is part one of the two part series on acyanotic congenital heart lesions which defines congenital heart disease, classifies it as cyanotic or acyanotic, describes pathophysiology of left-to-right shunts and reviews septal defects and patent ductus arteriosus. This podcast was developed by Herman Bami, a second year medical student from Schulich School of Medicine and Dentistry at the University of Western Ontario and Dr. Michael Grattan, a pediatric cardiologist at the London Health Sciences Center.