The Prayer of the Heart (also known as the Jesus Prayer) is a spiritual meditation in which you unite your mind with your heart by repeating a sacred prayer word - preferably repeating the NAME of God - to quiet the mind and experience the presence of God within you.
http://www.friendsinchrist.net/fic_jpry.shtml
A focus on personal spiritual prayer has long been a tradition in the spirituality of the Eastern Orthodox Church. An ancient, accepted prayer method has been the Jesus Prayer.
Its origins go back to the Old Testament belief that the Names of God carried Divine energy. This belief was carried forward by the first Christians' feeling about the name of Jesus (e.g. John 16:23-24, Acts 4:10)). Also, the early Christian monks who went out into the desert to live and pray in the second through the fourth centuries had a preference for short, repetitious prayer ("monological prayer"). The Orthodox Church has looked to these Desert Fathers as a major source of spiritual wisdom. A favorite repetitious prayer of these monks was Kyrie eleison (Lord, have mercy). By the sixth century, the statement of the tax collector in Luke 18:13 became the basis of the prayer. "God, have pity on me, a sinner."
Form and Method: A word or group of words is selected, usually with the aid of an elder.
Often, only the name of "Jesus" is used.
A widely accepted form is:
"Lord Jesus Christ, Son of God, have mercy on me, a sinner."
Some use only the words:
"Lord, have mercy."
Friends in Christ, Inc.Writings from the Philokalia: On Prayer of the Heart