Diastole is the phase of the cardiac cycle.
a. contraction
b. relaxation
c. monitoring
d. termination

Diastole is the relaxation phase of the cardiac cycle. It is the normal rhythmic dilation of the heart's valves. During this time, the valves start to gather blood inside of their chambers. There are two types of diastole that occur in the heart, and they are:

1. Ventricular diastole - this is the period where the ventricles are filling and relaxing. 
2. Atrial diastole - the period in which the atria are relaxing. 

This is a continuous cycle that occurs in the heart the moment a person is conceived until the person meets his/her death.