|MadSci Network: Medicine|
Dear Darin, The hole between the left and right side of the heart before birth is called the foramen ovale and allows blood to flow from the right atrium to the left atrium. At birth, this hole closes over and becomes a small scar called the fossa ovalis. If the foramen ovale fails to close at birth, this is not usually a problem as a valvelike flap prevents blood flow between the two atrial chambers when the lungs become functional. This information can be found in "Human Physiology" by Lauralee Sherwood, this book is an excellent introduction if you are interested in physiology.
Try the links in the MadSci Library for more information on Medicine.