Diastole is when the heart muscle relaxes. When the heart relaxes, the chambers of the heart fill with blood, and a person's blood pressure decreases.

Which part of the heart is in diastolic phase?

In diastole, both the atria and the ventricles are relaxed. Blood flows from the vena cava and pulmonary veins into the right and left atria respectively, before flowing directly into the ventricles.

Where does diastole happen?

Diastole, in the cardiac cycle, period of relaxation of the heart muscle, accompanied by the filling of the chambers with blood. Diastole is followed in the cardiac cycle by a period of contraction, or systole (q.v.), of the heart muscle.