Systems and methods sense electrical events in heart tissue to identify the location of an arrhythmogenic focus for ablation. The systems and methods establish a contact site between heart tissue and a curvilinear electrode array. The systems and methods monitor signals representing electrical events sensed by the electrodes in the contact site. The signals are displayed as graphic information that represents the time sequence in which the electrodes sense a given electrical event. By moving the electrode array to one or additional contact sites in the general direction of the electrode that first sensed the electrical event, the physician homes in on a contact site in which all electrodes on the array sense the given electrical event at generally the same time. This contact site contains the arrhythmogenic focus. The systems and methods convey ablating energy to bipolar pairs of the electrodes to form large bipolar lesions in heart tissue.