noun (n)

• a rapid and irregular heart beat(noun.state)

  source: wordnet30
• a shaky motion(noun.state)

  Synonym:
  quiver, quivering, shakiness, shaking, trembling, vibration
  

  source: wordnet30
• A rapid pulsation; a throbbing; esp., an abnormal, rapid beating of the heart as when excited by violent exertion, strong emotion, or by disease.(noun)

  source: webster1913