palpitation vs pit-a-pat

palpitation

noun
  • An abnormal beating of the heart that may be perceived by the patient, a result of excitement, exertion, or illness. 

pit-a-pat

noun
  • A series of quick tapping sounds 

adv
  • With a quick tapping sound 

verb
  • To make a series of quick tapping sounds; to palpitate 

How often have the words palpitation and pit-a-pat occurred in a corpus of books? (source: Google Ngram Viewer )