The Collaborative International Dictionary of English v.0.48:

Diastole \Di*as"to*le\, n. [L., fr. Gr. ?, fr. ? to put asunder,
   to separate; dia` through + ? to set, to place.]
   1. (Physiol.) The rhythmical expansion or dilatation of the
      heart and arteries; -- correlative to systole, or
      contraction.
      [1913 Webster]

   2. (Gram.) A figure by which a syllable naturally short is
      made long.
      [1913 Webster]

WordNet (r) 3.0 (2006):

diastole
    n 1: the widening of the chambers of the heart between two
         contractions when the chambers fill with blood

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "diastole":
   arsis, beat, bloat, bloatedness, bloating, blowing up, bout,
   circle, circuit, course, cycle, dilatation, dilation, distension,
   downbeat, dropsy, edema, flatulence, flatulency, flatus, gassiness,
   inflation, intumescence, meteorism, puff, puffiness, puffing,
   pulse, revolution, rotation, round, series, spell, stretching,
   swell, swellage, swelling, swollenness, systole, thesis,
   tumefaction, tumescence, tumidity, tumidness, turgescence,
   turgidity, turgidness, turn, tympanism, tympany, upbeat, wheel,
   windiness