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