A cardiac ablation instrument assembly comprising: a deflectable first catheter adapted for disposition within a heart having at least one lumen therein extending from a proximal end to a distal end, the catheter having a deflectable end section formed of a plurality of polymeric segments (b, c, d, e), at least one polymeric segment having a different stiffness as compared to another polymeric segment of the deflectable end section thereby allowing the deflectable end section to form a compound curve upon deployment and deflection within the heart; an elongate second catheter for disposition within a heart, the second catheter being at least partially contained within the first catheter; an expandable balloon member having a wall coupled to the elongate second catheter and sized for positioning proximate to a pulmonary vein; characterized by an ablation element within the balloon member for creating at least one lesion proximate the pulmonary vein by conveying energy through the balloon wall; wherein the ablation element is axially movable within an interior of the balloon member to permit the energy to be directed to target tissue by altering a location at which the energy is conveyed through the balloon member, wherein the ablation element is contained within an elongated body that moves axially within the second catheter and the balloon member; an endoscope that is also contained within the elongated body to permit viewing of the target tissue and assist in positioning of the ablation element; and wherein the lumen is sized and configured to allow passage of the elongate second catheter, the balloon member and the ablation element contained within the balloon member, and wherein the ablation element is operatively connected to a first translatory mechanism for positioning the ablation element at a selected location within the balloon member and the endoscope is operatively connected to a second translatory mechanism for positioning the endoscope within the balloon member, the endoscope being independently positionable relative to the ablation element, wherein said at least polymeric segment has a stiffness of 63D, the deflectable end section being in a range of 20 mm - 20 cm and the polymeric segment being in a range of 1 - 100 mm, said compound curve provides effective access to the superior and inferior pulmonary veins of the heart. a deflectable first catheter adapted for disposition within a heart having at least one lumen therein extending from a proximal end to a distal end, the catheter having a deflectable end section formed of a plurality of polymeric segments (b, c, d, e), at least one polymeric segment having a different stiffness as compared to another polymeric segment of the deflectable end section thereby allowing the deflectable end section to form a compound curve upon deployment and deflection within the heart; an elongate second catheter for disposition within a heart, the second catheter being at least partially contained within the first catheter; an expandable balloon member having a wall coupled to the elongate second catheter and sized for positioning proximate to a pulmonary vein; characterized by an ablation element within the balloon member for creating at least one lesion proximate the pulmonary vein by conveying energy through the balloon wall; wherein the ablation element is axially movable within an interior of the balloon member to permit the energy to be directed to target tissue by altering a location at which the energy is conveyed through the balloon member, wherein the ablation element is contained within an elongated body that moves axially within the second catheter and the balloon member; an endoscope that is also contained within the elongated body to permit viewing of the target tissue and assist in positioning of the ablation element; and wherein the lumen is sized and configured to allow passage of the elongate second catheter, the balloon member and the ablation element contained within the balloon member, and wherein the ablation element is operatively connected to a first translatory mechanism for positioning the ablation element at a selected location within the balloon member and the endoscope is operatively connected to a second translatory mechanism for positioning the endoscope within the balloon member, the endoscope being independently positionable relative to the ablation element, wherein said at least polymeric segment has a stiffness of 63D, the deflectable end section being in a range of 20 mm - 20 cm and the polymeric segment being in a range of 1 - 100 mm, said compound curve provides effective access to the superior and inferior pulmonary veins of the heart.