The Collaborative International Dictionary of English v.0.48:

Asystole \A*sys"to*le\, n. [Pref. a- not + systole.] (Physiol.)
   A weakening or cessation of the contractile power of the
   heart.
   [1913 Webster]

WordNet (r) 3.0 (2006):

asystole
    n 1: absence of systole; failure of the ventricles of the heart
         to contract (usually caused by ventricular fibrillation)
         with consequent absence of the heart beat leading to oxygen
         lack and eventually to death [syn: asystole, cardiac
         arrest, cardiopulmonary arrest]