A porous electrode, particularly a cardiac pacemaker electrode is described which is implantable in organic tissue. The electrode has a sintered member made of electrically conductive particles. In a portion of the electrode surface the particles are covered wtih a material of lower electrical conductivity than that of the particles. Another portion of the surface is coated with a metal inert to body fluids. Suitable materials for the particles are metals or alloys from the group containing tantalum, titanium, mobium, zirconium as well as cobalt-chromium-based alloys.