Orthodox churches have valid holy orders and apostolic succession through the episcopacy. Thus, their Eucharist is valid.
The *Catechism of the Catholic Church * says,
1399 “The Eastern churches that are not in full communion with the Catholic Church celebrate the Eucharist with great love. “These Churches, although separated from us, yet possess true sacraments, above all - by apostolic succession - the priesthood and the Eucharist, whereby they are still joined to us in closest intimacy.” A certain communion in sacris, and so in the Eucharist, “given suitable circumstances and the approval of Church authority, is not merely possible but is encouraged.”
838 “Those “who believe in Christ and have been properly baptized are put in a certain, although imperfect, communion with the Catholic Church.” With the Orthodox Churches, this communion is so profound “that it lacks little to attain the fullness that would permit a common celebration of the Lord’s Eucharist.”
844 “Catholic ministers may licitly administer the sacraments of penance, Eucharist and anointing of the sick to members of the oriental churches which do not have full Communion with the Catholic Church, if they ask on their own for the sacraments and are properly disposed. This holds also for members of other churches, which in the judgment of the Apostolic See are in the same condition as the oriental churches as far as these sacraments are concerned.”
- … “Eastern Christians who are in fact separated in good faith from the Catholic Church, if they ask of their own accord and have the right dispositions, may be admitted to the sacraments of Penance, the Eucharist and the Anointing of the Sick. Further, Catholics may ask for these same sacraments from those non-Catholic ministers whose churches possess valid sacraments, as often as necessity or a genuine spiritual benefit recommends such a course and access to a Catholic priest is physically or morally impossible.”
Unfortunately, the same cannot be said for Protestant churches (including Anglican/Episcopalian churches).
The *Catechism of the Catholic Church * states the following:
“Ecclesial communities derived from the Reformation and separated from the Catholic Church, “have not preserved the proper reality of the Eucharistic mystery in its fullness, especially because of the absence of the sacrament of Holy Orders.” It is for this reason that, for the Catholic Church, Eucharistic intercommunion with these communities is not possible. However these ecclesial communities, “when they commemorate the Lord’s death and resurrection in the Holy Supper . . . profess that it signifies life in communion with Christ and await his coming in glory.”
The Church teaches that when a person receives Communion in the Catholic Church, he thereby declares that he is fully at one with the Catholic Church in her belief. A non-Catholic cannot make this declaration, and so his receiving Communion would say something that is not true. It would not be honest. In the same way, if a Catholic were to receive Communion in the Anglican church or any other Protestant church, that person would be declaring his oneness with that denomination. And, that too, would be untrue.
Jimmy Akin’s article at
Who Can Receive Communion?
Pope Leo XIII’s *Apostolicae Curae * (Nullity of Anglican Orders)
Eastern Christianity: Ecumenical Links and Information