Accelerated idioventricular rhythm (AIVR) is a ventricular rhythm occuring at a rate between 41-100 / minute - faster than typical pacemaker rates expected of the ventricles (20-40 / minute) and less than what is considered a tachycardia (>100 / minute). Enhanced automaticity - possibly due to hypoxia or abundant sympathetic stimulation - increases rate of ventricular electrical impulses. Note that this rhythm is often unstable and can move quickly to either asystole or ventricular tachycardia (VT).