What happens to the pressure exerted on blood when the heart contracts? What happens to pressure exerted on the blood when the heart relaxes or the blood vessels dilate?

Contraction of heart increases blood pressure.

Relaxation of heart and vasodilation reduce the blood pressure.

Explanation:

Contraction of heart chambers increases the blood pressure while their relaxation and vasodilation lower down the blood pressure.

For example, during ventricular systole, maximum pressure is exerted by the contracting ventricles on the walls of the arteries leading to systolic (the peak) blood pressure while the pressure exerted on arterial walls is lowest when ventricle is relaxed.

Blood pressure is also affected by resistance of blood flow through vessels. The increased diameter of blood vessels reduces resistance and increases blood flow. The result is reduced blood pressure.