Abstract: An apparatus for providing both a read/pace mode of operation and a cardioversion/defibrillation (C/D) mode of operation utilizing common electrodes is disclosed that switches between the various modes. The apparatus incorporates a switch, such an electromechanical or electronic switch, that is used to control any number of poles and allow all of the electrode connections to be switched simultaneously. The apparatus further includes a set of intracardiac catheters or coils, which are inserted into the body intravenously to monitor the heart and to provide C/D to the patient. A second set of electrical contacts or electrode patches can provide exterior operation on a patient and the apparatus can operate with sufficient current and intensity to operate in this mode, as opposed to the intracardiac mode for the catheter electrodes. The switch enables proper selection of either set of electrodes as well as power source and intensity to achieve optimal results in treatment and monitoring of a patient's heart.