Which of the following factor is determined by preload?

Preload is the initial stretching of the cardiac myocytes prior to contraction; therefore, it is related to the sarcomere length at the end of diastole. Sarcomere length cannot be determined in the intact hea so indirect indices of preload, such as ventricular end-diastolic volume or pressure, must be used. Ref: Cardiovascular Physiology Concepts By Richard E. Klabunde, 2005, Page 69; Guyton's physiology 22nd edition, Page 111.