A code of three to five letters to describe pacemaker type and function. The first letter indicates the chamber(s) paced: V for ventricle pacing, A for atrial pacing, and D for dual chamber (i.e., both atrial and ventricular) pacing. The second letter indicates the chamber from which electrical activity is sensed (i.e., A for atrium, V for ventricle, or D for dual sensing). Other notations indicate the response to a sensed electrical signal: none, inhibition, triggering of pacing, and dual response that may inhibit or trigger pacing in the atrium, ventricle, or both.