**1. Introduction**

Cardiomyopathies represent a heterogenous group of myocardial diseases in which the myocardium exhibits structural and/or functional dysfunction [1, 2]. Current definition of cardiomyopathies excludes structural myocardial processes and dysfunction secondary to specific cardiovascular disorders such as coronary artery disease, systemic arterial hyperten‐

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sion, congenital heart diseases or valvular diseases. Although tachycardia-induced cardiomy‐ opathy may be seen as secondary due to well-defined causal cardiovascular factor, this disorder ranks among cardiomyopathies also in the current definition and classification of cardiomyopathies [1, 2].

Tachycardia-induced cardiomyopathy is a disease with attributes of dilated cardiomyopathy that develop as a consequence of persistent tachycardia. It is characterized by systolic ventric‐ ular dysfunction and dilatation with heart failure symptoms that occur as a result of long-term tachycardia of either supraventricular or ventricular origin. This disease should be also considered as a cause of ventricular dysfunction in the absence of tachycardia at the time of patient presentation since the tachyarrhythmia could disappear spontaneously before the initiation of patient examination, while the hemodynamic and especially structural changes of the heart induced by long-term tachycardia may persist even weeks after arrhythmia disappearance and/or rate control achievement.

The key feature of tachycardia-induced cardiomyopathy is the reversibility of both functional and structural changes as soon as the heart rate/rhythm is well controlled. In such case, improvement or even complete functional and structural normalization may be found. A correct diagnosis is thus often stated retrospectively based on the observation of ventricular systolic function improvement and regression of ventricular dilatation after appropriate rate/ rhythm control.
