fibrillating

/F IH0 B R IH0 L EY0 T IH0 NG/
verb
  1. 1

    To make rapid irregular movements.

adjective
  1. 1

    Splitting into fibrils or fibres.

  2. 2

    Of a muscle, especially in the heart: undergoing fibrillation; quivering.

Source: https://en.wiktionary.org/wiki/fibrillate, https://en.wiktionary.org/wiki/fibrillating