The Collaborative International Dictionary of English v.0.48:

Palpitant \Pal"pi*tant\, a. [L. palpitans, p. pr.]
   Palpitating; throbbing; trembling. --Carlyle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

palpitant
    adj 1: having a slight and rapid trembling motion; "palpitant
           movements rather than violent eruptions"; "my palpitating
           heart" [syn: palpitant, palpitating]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "palpitant":
   beating, clicking, drumming, fluttering, pitapat, pounding,
   pulsatile, pulsating, pulsative, pulsatory, pulsing, rhythmic,
   spattering, spluttering, sputtering, staccato, throbbing,
   thrumming, thumping, ticking