This is an interventional pilot study that proposes to evaluate the safety, logistical feasibility, and technological feasibility of using Fluorescite with fiberoptic confocal microscopy during cardiac surgery to discriminate between cardiac tissue and conduction tissue. During surgery to repair atrial septal defect, diluted Fluorescite will be added to the surface of the heart. The fiberoptic confocal microscope (Cellvizio 100 Series System with Confocal Miniprobe) will be used to record images in several different locations of the heart. The image files will be provided to blinded raters who will attempt to identify whether they contain cardiac tissue or conduction tissue. All subjects will be monitored while they are inpatient after surgery for any adverse events.