[Heart failure with mid-range ejection fraction. Looking for Middle Earth?].

The latest guidelines of the European Society of Cardiology have proposed a classification of heart failure based on left ventricular ejection fraction. Three distinct groups have been identified: heart failure with ejection fraction ≥50%, between 40 and 49%, and <40%. This classification has the advantage to be simple but it has been criticized because it is not clear whether the mid-range ejection fraction group is an independent category or just a transition phase between the other two groups. The purpose of this article is to discuss the characteristics and prognosis of mid-range ejection fraction heart failure on the basis of current evidence.