What is Heresy?
The ecumenical council of Ephesus affirms Catholicism by teaching the Filioque. "Filioque" means "and the Son" in Latin. The Eastern "Orthodox" reject this doctrine since they follow heresiarch Photius of the 9th century. The Church teaches the Filioque in several places, but the most renowned is its first dogmatic definition in the ecumcnial council of Florence: "...the holy Spirit is eternally from the Father and the Son, and has his essence and his subsistent being from the Father together with the Son, and proceeds from both eternally as from one principle and a single spiration." The council of Ephesus teaches this doctrine by saying that: "For even though the Spirit exists in his own hypostasis and is thought of on his own, as being Spirit and not as Son, even so he is not alien to the Son. He has been called the Spirit of truth [Jn. 16:13], and Christ is the truth [Jn. 14:6], and the Spirit was poured forth by the Son, as indeed the Son was poured forth from the God and Father." We can see St. Cyril liken the "pouring forth" of the Spirit from the Son to the "pouring forth" of the Son from the Father. Since he likens them, and the beggetting of the Son from the Father is eternal, this would make the spiration of the Spirit from the Son eternal, thus affirming the Catholic Filioque doctrine. The reason this affirms Catholicism is that Eastern "Orthodox" and Catholics both accept this council, thus the "Orthodox" are refuted by a council which they accept and put faith in.
"Orthodox" Objection: "The council teaches that papal primacy is false, for St. Cyril said: 'For Peter and John were equal in honour to each other, being both of them apostles and holy disciples, but they were two, not one.'"
Catholic Response: "The apostles Peter and John are equal in apostolic dignity. If a governor were the highest of governors, and he were to be called 'equal in honor to the others, being both of them governors,' there is no contradiction to his primacy or supremacy over the other governors."
Council quotes from papalencyclicals.net