During diastole, the left ventricle receives blood from the left atrium that is subsequently ejected into the systemic circulation. In simple terms, the efficiency of left ventricular (LV) filling can be measured as the ability to receive a large volume of blood at a rapid filling rate under low filling pressures. Numerous passive and active properties of the myocardial fibers together with physical-geometric properties contribute to the process of LV filling through three primary functions: LV relaxation, LV compliance, and left atrial function. Diastolic dysfunction and diastolic heart failure therefore occur as a consequence of impairment in any one or a combination of these.