Background. The MAZE-III is the surgical treatment of choice for medically refractory atrial fibrillation. Although a number of nonsurgical techniques are evolving to duplicate the transmural atrial lesions of the MAZE-III, the surgical atriotomy remains the gold standard for conduction block. It was the objective of this study to surgically create the atrial incisions of the MAZE-III without the use of cardiopulmonary bypass. Methods. A technique was developed to create and intersect the linear incisions of the MAZE-III on 10 beating canine hearts without the use of cardiopulmonary bypass using a 'tunnel' of atrial tissue. The effectiveness of the procedure was tested by atrial burst pacing. Results. This technique was successfully performed on 10 mongrel dogs without operative mortality. Preoperatively, sustained atrial fibrillation (> 30 seconds) was induced in all animals. Postoperatively, all the animals remained in sinus rhythm even after burst pacing. Conclusions. In an experimental canine model, the MAZE-III can be performed on beating hearts without the assistance of cardiopulmonary bypass using a 'tunnel' technique. This technique allows for the immediate assessment of electrophysiologic and mechanical function after the MAZE-III, or any other type of procedure using the 'maze principle' and may find future application in the clinical arena.