A device suitable for insertion into the pulmonary vein for the treatment of atrial fibrillation, the device comprising: at least one apertured lumen having distale and proximal ends; an inflatable balloon in the vicinity of the distal end of the lumen; an optical fiber at least partially within the at least one lumen and disposed along the axis of the lumen, the optical fiber being suitable for conveying a beam of laser energy; at least one opening in the vicinity of the distale end and within the inflatable balloon; an optical device in the lumen in the vicinity of the distale end and within the balloon to deflect a laser beam introduced in the vicinity of the proximal end and exiting in the vicinity of the distale end of the lumen at angles other than along the lumen axis, the lumen being rotatable around the lumen axis while the inflatable balloon remains stationary; a plurality of electrodes (12, 14, 42, 44, 30, 32, 302) formed on the balloon and suitable for one or both of measurement and treatment of the pulmonary vein wall, a controller operatively connected to the a plurality of electrodes; wherein, when the inflatable balloon is inflated, the electrodes (12, 14, 42, 44, 30, 32, 302) are adapted to come into contact with the pulmonary vein wall and operable for one or more of measurement and treatment; and laser energy is conveyable along the lumen axis to the optical device, the optical device being adapted to deflect the laser beam to impinge on the pulmonary vein wall, characterized by the deflected laser energy impinging on the pulmonary vein wall through a laser beam treatment area within the inflated balloon; and by the electrodes (12, 14, 42, 44, 30, 32, 302) being located outside the laser beam treatment area. at least one apertured lumen having distale and proximal ends; an inflatable balloon in the vicinity of the distal end of the lumen; an optical fiber at least partially within the at least one lumen and disposed along the axis of the lumen, the optical fiber being suitable for conveying a beam of laser energy; at least one opening in the vicinity of the distale end and within the inflatable balloon; an optical device in the lumen in the vicinity of the distale end and within the balloon to deflect a laser beam introduced in the vicinity of the proximal end and exiting in the vicinity of the distale end of the lumen at angles other than along the lumen axis, the lumen being rotatable around the lumen axis while the inflatable balloon remains stationary; a plurality of electrodes (12, 14, 42, 44, 30, 32, 302) formed on the balloon and suitable for one or both of measurement and treatment of the pulmonary vein wall, a controller operatively connected to the a plurality of electrodes; wherein, when the inflatable balloon is inflated, the electrodes (12, 14, 42, 44, 30, 32, 302) are adapted to come into contact with the pulmonary vein wall and operable for one or more of measurement and treatment; and laser energy is conveyable along the lumen axis to the optical device, the optical device being adapted to deflect the laser beam to impinge on the pulmonary vein wall, characterized by the deflected laser energy impinging on the pulmonary vein wall through a laser beam treatment area within the inflated balloon; and by the electrodes (12, 14, 42, 44, 30, 32, 302) being located outside the laser beam treatment area.