WITH progressive sophistication of the operative treatment of heart disease and expansion of operability limits to include more precariously ill patients, the problems of postoperative myocardial depression with increased rhythm instability have assumed increased importance. Surgeons at the University of Oregon and University of Illinois hospitals have been investigating the use of atrial pacing as one means of meeting these problems. Cardiologists and physiologists have employed atrial electrodes as experimental tools for the study of cardiac function,1 and subsequently in the clinical setting for the evaluation of complex arrhythmias and intracardiac shunts2,3 and for treating occasional cases of ventricular irritability.4,5 However, it was not until recently that the value of atrial pacing as a surgical adjuvant for maintaining optimum postoperative cardiac output and synchronous rhythm stability was first reported.6,7 Other authors have since described similar results with this technique,8,9 but heretofore no reports have attempted