An example device includes an elongated housing, a first and second electrode, and signal generation circuitry. The housing can be implanted within a single first chamber of the heart. The first electrode extends distally from the distal end of the elongated housing. A distal end of the first electrode can penetrate into wall tissue of a second chamber of the heart. The second electrode, extending from the distal end of the elongated housing, is configured to flexibly maintain contact with the wall tissue of the first chamber without penetration of the wall tissue of the first chamber by the second electrode. Signal generation circuitry can be within the elongated housing and coupled to the first and second electrode. The signal generation circuitry can deliver cardiac pacing to the second chamber via the first electrode and the first chamber via the second electrode.