Dear John:

The Jesus Prayer comes from the Hesychasm tradition of the Eastern hermits (from Eastern Orthodox and Eastern Catholic Byzantine traditions). The word Hesychasm means "quiet, stillness." The Hesychast tradition is a type of mystical prayer or meditation that is similar to some meditative forms in Buddhism, Hinduism, and even yoga, but it is not any of those traditions.

The Hesychasts take literally the teaching of Saint Paul's exhortation to the Thessalonians to "pray without ceasing" (1 Thess 5:1).  From the Catholic Encyclopedia:

Hesychasts (hesychastes -- quietist) were people, nearly all monks, who defended the theory that it is possible by an elaborate system of asceticism, detachment from earthly cares, submission to an approved master, prayer, especially perfect repose of body and will, to see a mystic light; which is none other than the uncreated light of God. The contemplation of this light is the highest end of man on earth; in this way is a man most intimately united with God. The light seen by Hesychasts is the same as appeared at Christ's Transfiguration. This was no mere created phenomenon, but the eternal light of God Himself. It is not the Divine essence; no man can see God face to face in this world (John i, 18), but it is the Divine action or operation. For in God action (energeia, actus, operatio) is really distinct from essence (ousia). There was a regular process for seeing the uncreated light; the body was to be held immovable for a long time, the chin pressed against the breast, the breath held, the eyes turned in, and so on. Then in due time the monk began to see the wonderful light.

The method of using the Jesus Prayer, which is, "Lord Jesus Christ, Son of God, have mercy on me, a sinner" is to breathe in when saying "Lord Jesus Christ, Son of God" and when breathing out saying "have mercy on me, a sinner." This prayer form is said constantly throughout the waking hours, often using a special knotted prayer rope or beads design for this prayer.

These hermits will be saying this prayer even when they are talking to others. It is said the older hermits even pray this prayer when they are asleep.

This form of prayer is rigorous and must not be tried without a spiritual director who is qualified to help a person in this way of life.

As to your second question, the Orthodox Churches are considered by the Catholic Church to be genuine Churches with apostolic succession and valid sacraments. Thus, when an Orthodox person cannot receive the Sacraments from his own Church he may receive the Sacraments in a Catholic Church (CIC 844.3) if he requests it and is otherwise properly disposed.

The Orthodox, however, are not in communion with the Catholic Church since they do not accept the Pope. They are not heretics, but they are in what is called "material schism". Material schism means that while the current Orthodox Churches today have not committed a specific act of schism, they are in "technical" schism because they do not accept the authority of the Pope. The original Bishops who split from the Catholic Church a thousand years ago are the ones who committed an act of schism.

The word "heretic" refers to a Catholic who chooses to deny some element of Catholic faith that is required for belief by all Catholics. One has to be Catholic to be a heretic. Orthodox and Protestants are not Catholic so they do not technically qualify for the term "heretic" no matter what beliefs they have.

Again, for Protestants and perhaps some Orthodox beliefs the term "material heresy" applies -- meaning that a technical heresy may be held by the ecclesial group though the current members of that ecclesial group have not made any personal decisions to adopt a heresy. Those who were never Catholic, such as Orthodox, Anglican, Protestant, etc. grow up with the beliefs of their communities, which may hold views that are considered heretical by the Catholic Church, but they themselves are not heretics as they know only what they have been taught by their denomination.

God Bless,
Bro. Ignatius Mary