In cardiovascular physiology, end-diastolic volume (EDV) is the volume of blood in the right or left ventricle at the end of filling during diastole, the relaxation phase of the cardiac cycle. Because greater EDVs cause greater distention of the ventricle, EDV is often used synonymously with preload, which refers to the length of the sarcomeres in cardiac muscle prior to contraction (systole). An increase in EDV increases the preload on the heart and, through the Frank-Starling mechanism of the heart, increases the amount of blood ejected from the ventricle during systole.