Para-esophageal anastomosis of left atrium was examined in orthotopic heart transplantation as a new surgical technique for transesophageal electrophysiologic study of the transplanted heart. Seven orthotopic heart transplantations were performed in mongrel dogs. Left atrial appendage of the donor heart was trimmed as a flap and the sinus venosus of right atrium was incised posteriorly. An upper midline incision was made in the posterior wall of left atrium of the recipient after native ventricles were resected. Left atrial appendage flap of the donor heart was anastomosed to the posterior incision of native left atrium, and the remains of left atrium were sutured continuously. Sinus venosus incision of the donor heart was anastomosed to the right atrium of recipient. Ascending aorta and pulmonary trunk were reconstructed in the standard fashion. Transesophageal atrial pacing was possible during and after weaning from cardiopulmonary bypass in all seven cases. The appendage flap was found to occupy one third of the posterior wall of left atrium at the time of sacrifice. It was suggested that para-esophageal anastomosis of left atrium would be an useful technique for transesophageal electrophysiologic study of the transplanted heart.