If the right ventricle begins to pump an increased amount of blood, this soon arrives at the left ventricle, stretches it more than before, and causes it to increase its stroke volume and match that of the right. this is and example of

This question has choices namely:

preload
afterload
contractility
cardiac reserve

The correct answer is preload. Preload is the filling capacity of the heart and it corresponds to the volume of the blood that fills the ventricles during a cycle. In this case, the left ventricle needs to accommodate the increased volume from the right heat therefore increasing the filling capacity therefore the preload. 

Afterload is the pressure that the heart needs to overcome to pump the blood. In the right ventricle, the pressure is the pulmonary arteries wherein the right ventricle needs to contract and generate a pressure greater than the pulmonary arteries for the blood to move out the ventricle. Similarly, in the left ventricle, the source of pressure is the aorta and the left ventricle needs to contract and generate a pressure greater than the aorta and the systemic circulation for the blood to move out of the ventricle. 

Contractility is the force of contraction of each ventricle in one cycle.