The Orthodox are considered "Sister Churches" to the Catholic Church.  The Catholic Church recognizes ALL of their sacraments---including ordination to the priesthood and the Eucharist as VALID.  I am using the plural in referring to the Orthodox churches because their leadership comes from the Patriarchs---who are the successors of the Apostles, other than Peter.

Information from Unitatis Redintegration---Chapter Three [The Decree on Ecumenism---Nov. 21, 1964].