The Collaborative International Dictionary of English v.0.48:

Pitapat \Pit"a*pat`\, adv. [An onomatopoetic reduplication of
   pat a light, quick blow.]
   In a flutter; with palpitation or quick succession of beats.
   --Lowell. "The fox's heart went pitapat." --L'Estrange.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pitapat \Pit"a*pat`\, n.
   A light, repeated sound; a pattering, as of the rain. "The
   pitapat of a pretty foot." --Dryden.
   [1913 Webster]