An over-the-wire electrophysiology catheter which has an emitting electrode on the distal tip electrically connected to a source of high frequency electrical energy. The intravascular device is configured to be advanced through a patient's cardiac veins or coronary arteries and preferably is also provided with sensing electrodes for detecting electrical activity of the patient's heart from within a blood vessel of the heart. The device forms large lesions in tissue adjacent to the blood vessel in which the device is located without significantly damaging the blood vessel to effectively terminate signals causing arrhythmia.