A catheter for treating occlusions in blood vessels comprising: a tubular guidewire sheath defining a plurality of lumens, the plurality of lumens comprising a first lumen for carrying a guidewire; a shock wave generator located near a distal end of the catheter, said shock wave generator including at least one distal electrode pair, with electrodes of each pair being spaced apart to define at least one gap; a first wire and a second wire, wherein proximal ends of the first wire and the second wire are connectable to a pulsed voltage source, and wherein distal ends of the first wire and the second wire are connected to the at least one distal electrode pair such that when high voltage pulses are applied across the first wire and the second wire, current flows across the at least one gap creating shock waves for treating an occlusion; and a flexible cap (18, 280, 380) formed from a material having elastomeric properties and sealably attached to the distal end of the catheter and surrounding the at least one electrode pair, said flexible cap (18, 280, 380) being inflatable with conductive fluid such that the flexible cap (18, 280, 380) expands to provide a space between an inner wall of the flexible cap (18, 280, 380) and the at least one electrode pair and wherein when the flexible cap (18, 280, 380) is in a deflated state, a surface area of the flexible cap (18, 380) is small enough that the flexible cap (18, 280, 380) is not folded when the catheter is advanced into a blood vessel and when the flexible cap (18, 280, 380) is in an inflated state, a maximum diameter of the flexible cap (18, 280, 380) is no more than 15% greater than a diameter of the flexible cap (18, 280, 380) in a deflated state and wherein after being deflated, the flexible cap (18, 280, 380) is configured to return to a low profile configuration such that the flexible cap is not folded when removing the catheter from the blood vessel. a tubular guidewire sheath defining a plurality of lumens, the plurality of lumens comprising a first lumen for carrying a guidewire; a shock wave generator located near a distal end of the catheter, said shock wave generator including at least one distal electrode pair, with electrodes of each pair being spaced apart to define at least one gap; a first wire and a second wire, wherein proximal ends of the first wire and the second wire are connectable to a pulsed voltage source, and wherein distal ends of the first wire and the second wire are connected to the at least one distal electrode pair such that when high voltage pulses are applied across the first wire and the second wire, current flows across the at least one gap creating shock waves for treating an occlusion; and a flexible cap (18, 280, 380) formed from a material having elastomeric properties and sealably attached to the distal end of the catheter and surrounding the at least one electrode pair, said flexible cap (18, 280, 380) being inflatable with conductive fluid such that the flexible cap (18, 280, 380) expands to provide a space between an inner wall of the flexible cap (18, 280, 380) and the at least one electrode pair and wherein when the flexible cap (18, 280, 380) is in a deflated state, a surface area of the flexible cap (18, 380) is small enough that the flexible cap (18, 280, 380) is not folded when the catheter is advanced into a blood vessel and when the flexible cap (18, 280, 380) is in an inflated state, a maximum diameter of the flexible cap (18, 280, 380) is no more than 15% greater than a diameter of the flexible cap (18, 280, 380) in a deflated state and wherein after being deflated, the flexible cap (18, 280, 380) is configured to return to a low profile configuration such that the flexible cap is not folded when removing the catheter from the blood vessel.