Re: Babies Heart

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.