The atria are thin-walled chambers whose electromechanical and endocrine role is of critical relevance for the overall heart functioning. First of all, the atria act as a reservoir during ventricular systole, a conduit for blood transiting from veins to the ventricles, an active contractile chamber that augments left ventricular (LV) and right ventricular (RV) filling in late diastole and a suction source that refills itself in early systole. Through these various mechanical functions, the atria modulate ventricular filling [1, 2]. Particularly, atria reservoir function is mainly determined by atrial compliance/stiffness and is influenced by the base descent during systole and breathing phases; also, RV generates a driving pressure transmitted through the pulmonary circulation to help left atrium (LA) filling, while the systemic venous return is determined by a peripheral-to-central pressure gradient. Atria conduit function is inversely related to reservoir function and is strongly modulated by ventricular lusitropy. Atrial pump function, as for each cardiac chamber, is dependent on contractility, preload (venous return) and afterload (LV and RV end-diastolic pressure). Of note, the Frank–Starling law applies to atrial mechanics as well, with atrial emptying fraction increasing as atrial filling volume increases, in a non-linear fashion because of a drop in contractility after a certain degree of dilation [3].