The Collaborative International Dictionary of English v.0.48:

Perisystole \Per`i*sys"to*le\, n. [Pref. peri- + systole: cf. F.
   p['e]risystole.] (Physiol.)
   The interval between the diastole and systole of the heart.
   It is perceptible only in the dying.
   [1913 Webster]