The Collaborative International Dictionary of English v.0.48:

Palpitation \Pal`pi*ta"tion\, n. [L. palpitatio: cf. F.
   palpitation.]
   A rapid pulsation; a throbbing; esp., an abnormal, rapid
   beating of the heart as when excited by violent exertion,
   strong emotion, or by disease.
   [1913 Webster]

WordNet (r) 3.0 (2006):

palpitation
    n 1: a rapid and irregular heart beat
    2: a shaky motion; "the shaking of his fingers as he lit his
       pipe" [syn: shaking, shakiness, trembling, quiver,
       quivering, vibration, palpitation]