An increase in contractility is demonstrated on a Frank-Starling diagram by

The frank-starling law of the hea states that when increased quantities of blood flow into the hea, the increased blood stretches the walls of the hea chambers. As a result of the stretch, the cardiac muscle contracts with increased force, and this action empties the extra blood that has entered from the systemic circulation. For the hea, the length of the muscle fibers (ie, the extent of the preload) is propoional to the end-diastolic volume.