A transvenous lead system for cardiac stimulation with a pacemaker or implantable defibrillator having automatic activation of a passive fixation system. The lead includes an insulative lead body such as silicone rubber and has a proximal end with a connector for coupling the lead to the pacemaker or defibrillator. At least one conductor extends through the lead body for connection to a lead electrode. The lead further includes a plurality of flexible tines. In a first position, the tines are folded back along the lead body and exhibit a minimal profile. A hydrophilic material such as a hydrogel is disposed on the under side of each tine either as part of the tine or between the tine and the lead body. Upon exposure to body fluids when the lead is implanted, the hydrogel absorbs liquid and expands. This expansion forces the tines into a second, deployed position where the tines can engage trabeculae of the heart chambers to anchor the lead in place.