Abstract: A medical electrical lead which features a portion of the lead body which may be made temporarily stiff. The lead preferred is designed for implantation into a body and would include electrodes for both the ventricle and the atrium. The temporarily stiff portion may be located along the lead body in the area strictly within the atrium or may also include portions of the lead body implanted in the ventricle or even in the superior vena cava. The atrial portion further includes one or more electrodes. The temporarily stiff portion is formed through the use of a cavity in the lead body filled with magnet-rheologic fluid (hereinafter called "MRF"). Once the lead is implanted, a magnet may be used to communicate with the lead body and, in particular, with the MRF filled cavity. While in the magnetic field, the MRF will become solid and the lead body in such an area will become stiffer.