di·as·to·le 
(dī-ăstə-lē)
(dī-ăstə-lē)n.
1. Physiology The normal rhythmically occurring relaxation and dilatation of the heart chambers, especially the ventricles, during which they fill with blood.
2. The lengthening of a normally short syllable in Greek and Latin verse.
[Greek diastolē, dilation, separation, from diastellein, to expand : dia-, apart; see DIA- + stellein, to place, send; see stel- in the Appendix of Indo-European roots.]
di′as·tolic (dī′ə-stŏlĭk) adj.