A catheter-based medical device for ablating a blood vessel, the device comprising: an elongate catheter shaft including a liquid delivery lumen therethrough, wherein the liquid delivery lumen is configured for connection to an external liquid pharmacological agent source; a balloon device (381; 382) disposed at a distal end portion of said catheter shaft, said balloon device comprising an outer surface and an inner surface, said inner surface defining an interior space of said balloon device, said balloon device in fluid communication with said liquid delivery lumen, said balloon device comprising a porous or microporous material that is arranged to transmit the liquid pharmacological agent through said porous or microporous material, wherein said balloon device has a bulbous-shaped proximal portion and a generally cylindrical-shaped distal portion when said balloon is inflated, and wherein said bulbous-shaped proximal portion and said generally cylindrical-shaped distal portion are in fluid communication; one or more electrodes that are disposed on or within said balloon device and are arranged to deliver energy to the blood vessel, wherein said one or more electrodes is a single electrode disposed on said catheter shaft and in said interior space or wherein said one or more electrodes is a plurality of electrodes disposed on said outer surface, characterised in that said one or more electrodes comprises (i) a single electrode disposed on said catheter shaft and in said interior space and (ii) plurality of electrodes disposed on said outer surface; and that the device comprises a filter device, said filter device being deployable from said catheter shaft and generally coaxial with said balloon device, wherein a distal end portion of said filter device is configured to contact tissue surrounding an ostium of the blood vessel, wherein said filter device is arranged to be configured in a collapsed low-profile configuration and can reconfigure to an expanded configuration, and wherein at least a portion of said filter device is configured to surround said bulbous-shaped proximal portion when said filter device is in an expanded configuration and provide embolic protection. an elongate catheter shaft including a liquid delivery lumen therethrough, wherein the liquid delivery lumen is configured for connection to an external liquid pharmacological agent source; a balloon device (381; 382) disposed at a distal end portion of said catheter shaft, said balloon device comprising an outer surface and an inner surface, said inner surface defining an interior space of said balloon device, said balloon device in fluid communication with said liquid delivery lumen, said balloon device comprising a porous or microporous material that is arranged to transmit the liquid pharmacological agent through said porous or microporous material, wherein said balloon device has a bulbous-shaped proximal portion and a generally cylindrical-shaped distal portion when said balloon is inflated, and wherein said bulbous-shaped proximal portion and said generally cylindrical-shaped distal portion are in fluid communication; one or more electrodes that are disposed on or within said balloon device and are arranged to deliver energy to the blood vessel, wherein said one or more electrodes is a single electrode disposed on said catheter shaft and in said interior space or wherein said one or more electrodes is a plurality of electrodes disposed on said outer surface, characterised in that said one or more electrodes comprises (i) a single electrode disposed on said catheter shaft and in said interior space and (ii) plurality of electrodes disposed on said outer surface; and that the device comprises a filter device, said filter device being deployable from said catheter shaft and generally coaxial with said balloon device, wherein a distal end portion of said filter device is configured to contact tissue surrounding an ostium of the blood vessel, wherein said filter device is arranged to be configured in a collapsed low-profile configuration and can reconfigure to an expanded configuration, and wherein at least a portion of said filter device is configured to surround said bulbous-shaped proximal portion when said filter device is in an expanded configuration and provide embolic protection.