**1. Introduction**

Mechanical alternans (MA) is a mysterious phenomenon. MA, a condition characterized by beat-to-beat oscillation in the strength of cardiac muscle contraction at a constant heart rate, has been observed in patients with severe heart failure and in animal models of this condition. Although MA is rare under resting conditions in individuals with controlled heart failure, at higher heart rates it is more prevalent and likely to be sustained, as exemplified by pacinginduced MA or dobutamine-induced MA. However, few studies have addressed the clinical implications of dobutamine-induced MA in patients with heart failure. We therefore prospec‐ tively examined and compared the prognostic value of dobutamine- and pacing- induced MA in ambulatory patients with idiopathic dilated myocardiopathy (IDCM) in sinus rhythm.[1] Furthermore, this review addresses the clinical circumstances, relevance of MA, current understanding with ideas about its mechanism, and some future perspectives.
