Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

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}]