An atrial lead system providing single electrode bi-atrial pacing. The system includes an atrial pacing lead having electrode (12) located on a distal portion thereof and a guide catheter having a longitudinal lumen and a lateral aperture (104) open to the longitudinal lumen of the catheter proximal to a distal end of the catheter through which the distal portion of the lead may be advanced. The electrode is preferably an active fixation electrode device. First the guide catheter is advanced to the ostium of a patient's coronary sinus and the distal end of the guide catheter is inserted into the coronary sinus such that the lateral aperture (104) of the catheter is located in the patient's right atrium. The atrial pacing lead is then advanced through the lumen of the guide catheter such that the electrode exits the lateral aperture of the guide catheter and the electrode is affixed to the tissue of the atrial septum.