The Maze procedure was developed for the treatment of atrial fibrillation over a period of several years. Extensive experimental and clinical studies of the underlying electrophysiology of the arrhythmia were performed, and numerous surgical techniques and principles were tried before the Maze procedure was conceived. Few cardiac surgical procedures have undergone more extensive research and experimental trials before being applied clinically. This article gives a brief summary of the work leading up to the eventual Maze-III procedure that is now in clinical use.