Accelerated idioventricular rhythm (AIVR) was first described by Thomas Lewis in 1910.[1]AIVR is currently defined as an enhanced ectopic ventricular rhythm with at least 3 consecutive ventricular beats, which is faster than normal intrinsic ventricular escape rhythm (≤40 bpm), but slower than ventricular tachycardia (at least 100-120 bpm).[1]Importantly, there is rate overlap between AIVR and some slow ventricular tachycardia. AIVR should not be diagnosed solely based on ventricular rate. Other characteristics of AIVR are helpful for its correct diagnosis (see Differentials).