Slackening phase of the heart after contraction phase. After ejection of the blood from the ventricles, the internal pressure in the heart drops below that of the aorta and en|pulmonary artery, closing the pocket valves. As a result of the suction created by lowering the valve plane into the aphoria, the atria have filled again and the filling phase of the ventricles can begin.
https://de.wikipedia.org/wiki/Diastole (Wikipedia CC-by-sa-3.0)