Permanent pacemaker implantation is most commonly performed via the left or right subclavian or axillary vein. A cephalic vein may be used, and although it has advantages this approach has limitations. If the leads are inserted by either of these routes then the generator is placed between the subcutaneous fat and the surface of pectoralis major muscle in a prepectoral pocket. In very thin or emaciated patients or in those who wish the generator to be hidden completely from view, the generator may be placed behind the pectoralis muscle. An alternative site is the axilla, but this is rarely used. Epicardial devices are usually buried behind the rectus abdominis muscle. In patients with an occluded superior vena cava, pacing electrodes can be inserted via a femoral vein and the generator buried subcutaneously in the lower abdominal wall.