The electrochemical behavior, interfacial properties, and stability of RuO2-, IrO2-, (Ru1-xMnx)O-2- and (Ir1-xMnx)O-2-coated electrodes for pacemaker applications were investigated in a phosphate buffered saline solution, by electrochemical impedance spectroscopy and cyclic voltammetry (CV). The psuedocapacitive properties of these conducting oxides and influence of coating roughness and porosity were examined, and accelerated aging of the electrode materials was simulated by fast sweep rate CV cycles between -3 to 1 V vs. Ag/AgCl. Changes in surface composition and structure due to the accelerated aging were investigated using X-ray photoelectron spectroscopy and scanning electron microscopy. The conducting oxides exhibit high interfacial capacitance. At high sweep rates, not all of total capacitance could be utilized due to voltage drop associated with resistance down the pores. Above a certain sweep rate, the charging/discharging mechanism changes from capacitive to resistive character. Showing the best performance among the investigated materials, the RuO2 exhibits capacitive characteristics at sweep rates up to 20 V/s and excellent stability under the accelerated aging. The IrO2 coating was not stable during the cycling. The mixed oxides experience limitations at high sweep rates due to the ohmic effects and some degradation due to the accelerated aging. (c) 2005 The Electrochemical Society. All rights reserved.