An apparatus, comprising: a voltage pulse generator configured to produce a pulsed voltage waveform; and an electrode controller configured to be operably coupled to the voltage pulse generator and a medical device including a plurality of electrodes, the electrode controller including: a feedback module configured to determine an impedance between electrodes from the plurality of electrodes using current flowing between two opposite sides on an outer side of a heart, the current flowing through cardiac wall tissue of the heart at the two opposite sides and through intervening blood in a cardiac chamber in a direction from one side of the two opposite sides towards the other side of the two opposite sides; a selection module configured to: select a subset of electrodes from the plurality of electrodes based on the impedance; and identify at least a first electrode from the subset of electrodes as an anode and at least a second electrode from the subset of electrodes as a cathode; and a pulse delivery module configured to deliver an output signal associated with the pulsed voltage waveform to the subset of electrodes. a voltage pulse generator configured to produce a pulsed voltage waveform; and an electrode controller configured to be operably coupled to the voltage pulse generator and a medical device including a plurality of electrodes, the electrode controller including: a feedback module configured to determine an impedance between electrodes from the plurality of electrodes using current flowing between two opposite sides on an outer side of a heart, the current flowing through cardiac wall tissue of the heart at the two opposite sides and through intervening blood in a cardiac chamber in a direction from one side of the two opposite sides towards the other side of the two opposite sides; a selection module configured to: select a subset of electrodes from the plurality of electrodes based on the impedance; and identify at least a first electrode from the subset of electrodes as an anode and at least a second electrode from the subset of electrodes as a cathode; and a pulse delivery module configured to deliver an output signal associated with the pulsed voltage waveform to the subset of electrodes. a feedback module configured to determine an impedance between electrodes from the plurality of electrodes using current flowing between two opposite sides on an outer side of a heart, the current flowing through cardiac wall tissue of the heart at the two opposite sides and through intervening blood in a cardiac chamber in a direction from one side of the two opposite sides towards the other side of the two opposite sides; a selection module configured to: select a subset of electrodes from the plurality of electrodes based on the impedance; and identify at least a first electrode from the subset of electrodes as an anode and at least a second electrode from the subset of electrodes as a cathode; and select a subset of electrodes from the plurality of electrodes based on the impedance; and identify at least a first electrode from the subset of electrodes as an anode and at least a second electrode from the subset of electrodes as a cathode; and a pulse delivery module configured to deliver an output signal associated with the pulsed voltage waveform to the subset of electrodes. <EOS>