BECAUSE the last few years have shown that surgical attack on interauricular septal defects in the human has now become a matter of practical concern, it is well to learn from the laboratory as much as possible about the patterns of healing which ensue when interatrial openings are closed surgically in experimental animals.
In previous publications we have described the experimental background and clinical application of a surgical technique, using an atrial "well," which affords access to all portions of the interatrial septum.* By means of this method, precise manipulations can be carried out within the interior of the heart so that atrial septal defects can be created and may then be closed despite considerable variation in size and location of the openings. This affords an opportunity to study different methods of closing such defects and to compare the different patterns of healing at appropriate intervals after repairs. A comparative