A shock wave device comprising: an axially extending elongate member configured to be advanced through a blood vessel to treat a calcified lesion; a first electrode assembly comprising a first electrode pair and a second electrode pair, wherein the first electrode assembly is carried by the elongate member and positioned within a conductive fluid; and a controller coupled to the first electrode assembly , wherein the controller is configured to deliver a series of individual voltage pulses to the first electrode assembly such that each of the voltage pulses creates a shock wave in the conductive fluid to treat the calcified lesion, wherein the controller includes a voltage source having a constant polarity followed by a voltage polarity switch for switching the polarity of the voltage source and causing current to flow through the electrode assembly in a first direction for some of the pulses in the series and in a second direction opposite the first direction for the remaining pulses in the series and wherein the voltage polarity switch only operates between the delivery of individual voltage pulses so each voltage pulse delivered to the electrode assembly has a single direction of current flow wherein a first electrode in each of the first and second electrode pairs is coupled to the voltage polarity switch and wherein the second electrode in the first electrode pair is coupled to the second electrode of the second electrode pair and wherein the first electrode in each of the first and second electrode pairs has a surface area smaller than a surface area of the associated second electrode in the first and second electrode pairs. an axially extending elongate member configured to be advanced through a blood vessel to treat a calcified lesion; a first electrode assembly comprising a first electrode pair and a second electrode pair, wherein the first electrode assembly is carried by the elongate member and positioned within a conductive fluid; and a controller coupled to the first electrode assembly , wherein the controller is configured to deliver a series of individual voltage pulses to the first electrode assembly such that each of the voltage pulses creates a shock wave in the conductive fluid to treat the calcified lesion, wherein the controller includes a voltage source having a constant polarity followed by a voltage polarity switch for switching the polarity of the voltage source and causing current to flow through the electrode assembly in a first direction for some of the pulses in the series and in a second direction opposite the first direction for the remaining pulses in the series and wherein the voltage polarity switch only operates between the delivery of individual voltage pulses so each voltage pulse delivered to the electrode assembly has a single direction of current flow wherein a first electrode in each of the first and second electrode pairs is coupled to the voltage polarity switch and wherein the second electrode in the first electrode pair is coupled to the second electrode of the second electrode pair and wherein the first electrode in each of the first and second electrode pairs has a surface area smaller than a surface area of the associated second electrode in the first and second electrode pairs. <EOS>