Abstract: An apparatus for placing a pacing electrode in the coronary sinus so as to pace the left ventricle of the heart comprises a preshaped, flexible catheter having a distal end and a predetermined shape in an unflexed or steady state condition to facilitate placement of a distal end into the os of the coronary sinus within the right atrium of the heart. The catheter includes a first lumen which extends from an entry port at the proximal end of the catheter end of the catheter, through the catheter and terminating at an exit port at the distal end of the catheter. The catheter also includes a second lumen which extends from a first port in the vicinity of the proximal end of the catheter through the catheter and terminating at a second port which is in fluid communication with an inflatable/deflatable balloon in the vicinity of the distal end of the catheter. An inflating/deflating device, such as a syringe, is attachable to the first port of the second lumen of the catheter, for inflating/deflating the balloon.