A catheter assembly comprises a first branch body having a first axis, a second branch body extending in a non-parallel relationship with respect to the first axis, and at least one electrode carried by the second branch body. In use, the first branch body can be located within a pulmonary vein within the left atrium, while the electrode carried by the second branch body is located in contact with endocardial tissue outside the pulmonary vein. Ablation energy can be transmitted from the electrode to contacted endocardial tissue while the first branch body is located within the pulmonary vein.