A base cardiac electrogram signal at a base electrode is recorded for a predetermined amount of time. A plurality of cardiac electrogram signals at a plurality of electrodes other than the base electrode are recorded for the predetermined amount of time. The base cardiac electrogram signal is compared with each of the plurality of cardiac electrogram signals. The similarities between the base cardiac electrogram signal and each of the plurality of cardiac electrogram signals is determined. A specific area of cardiac tissue where the base electrode is positioned is mapped based at least in part on the determined similarities.