Pope Shenouda III
Prayer is the work of the heart, whether expressed in words or not.
  It is lifting up the heart to God because  the  heart talks to God through feelings and emotions more than the mouth   does with words. The heart may be lifted up to God without words.
  Therefore, the sigh of the heart is a  prayer before God,  The  heart’s longing to God is a prayer. Feelings of  love towards God are a  prayer. So prayer is a relationship between God  and man. And if this  hearty relationship does not exist, words would be  of no use.