Cardiac needle (plunge) electrode arrays are constructed utilizing integrated-circuit fabrication techniques. These plunge electrodes can be made up to two orders of magnitude smaller in cross-sectional area compared to conventional handmade electrodes. A method has been developed to measure potential gradients from arrays of electrodes formed by bonding two T-shaped probes back-to-back. The recording sites are situated on the vertical part of the T, and the larger bonding pads and connector wires are on the horizontal part. When inserted for recording, the horizontal portion of the probe is pulsed flush to the epicardial surface. Three sets of bipolar pairs are arranged along each vertical shaft. The bipolar pairs are spaced 2.5 mm apart with a 1-mm intercontact spacing. By recording signals with both the array's initial placement and after a 90° rotation of the back-to-back T arrangement, potential measurements are acquired in three mutually orthogonal directions yielding a three-dimensional configuration. Based on the differences in these potential measurements, more accurate potential gradient calculations can be obtained.