A ventricular septal defect (VSD) is a hole in the septum separating the left and right ventricles of the heart. VSDs are the most common type of congenital heart defect, occurring in about 2 out of every 1000 live births. They can range from small to large in size. Echocardiography is the primary way to diagnose a VSD and determine its location and size. Small VSDs may close on their own, but larger defects often require surgery to repair.