The Collaborative International Dictionary of English v.0.48:

Systole \Sys"to*le\, n. [NL., fr. Gr. ?, fr. ? to contract; sy`n
   with + ? to set, place.]
   1. (Gram.) The shortening of the long syllable.
      [1913 Webster]

   2. (Physiol. & Biol.) The contraction of the heart and
      arteries by which the blood is forced onward and the
      circulation kept up; also, the contraction of a
      rhythmically pulsating contractile vacuole; -- correlative
      to diastole. -- Sys*tol"ic, a.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

systole
    n 1: the contraction of the chambers of the heart (especially
         the ventricles) to drive blood into the aorta and pulmonary
         artery

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "systole":
   abbreviation, arsis, astriction, astringency, beat, bottleneck,
   bout, cervix, circle, circuit, circumscription, coarctation,
   compactedness, compaction, compression, compressure, concentration,
   condensation, consolidation, constriction, constringency,
   contraction, contracture, course, curtailment, cycle, decrease,
   diastole, diminuendo, downbeat, hourglass, hourglass figure,
   isthmus, knitting, narrow place, narrowing, neck, puckering, pulse,
   pursing, reduction, revolution, rotation, round, series,
   shortening, solidification, spell, stranglement, strangulation,
   striction, stricture, thesis, turn, upbeat, wasp waist, wheel,
   wrinkling