The three-position ICHD code designating pacemaker function has been widely adopted. A revision, expanding the code from three to five positions, incorporates the first three positions as in the earlier version, but includes position IV, programmable functions, and position V, tachyarrhythmia functions. The code indicates how the pacemaker is employed, not necessarily the purpose for which it was designed. For example, a single-chamber inhibited pulse generator with multiprogrammable capabilities which interrupts a tachycardia by a burst of rapid pacing is designated as VVI,MB if placed in the ventricle, and AAI,MB if in the atrium.