Five AP Biology students of Christina Signorelli  went to see how a heart surgery is performed at Allegheny General Hospital recently, according to Beaver County Radio News Correspondent Sandy Giordano.  Allison Kindred, a senior , said Dr. Stephen A. Bailey  replaced a man’s heart valve in approximately 4 hours, and the students  were permitted see the entire procedure.  A question and answer period followed. Dr. Bailey  is the division director of cardiac surgery at AGH., and  surgical director of cardiac transplantation. Mrs. Signorelli said the students  can take the class for a   college credit and  it will count at the end of the year.  Kindred plans to major in finance at PSU University Park. The students will visit the Pittsburgh Zoo and Aquarium on April 24.