The Filioque controversy has a few key points I’d like to discuss: first, the third ecumenical council of Ephesus, held in 431, quoted the creed from the first ecumenical council of Nicaea (held in 325, which doesn’t mention anything related to procession) and NOT the creed as stated in the second ecumenical council of Constantinople (held in 381, which does mention procession of the Holy Spirit from the Father), so using the seventh cannon of the third ecumenical council in the most orthodox and rigid interpretation would mean you also have to reject the creed of 381 stated in Constantinople. This clearly hasn’t been the case, as the East readily adopted the 381 creed liturgically.
Second, even as early as 410, before the council of Toledo of 447, in the East we find that the Council of Seleucia-Ctesiphon had already introduced “and the Son” into the Nicene Creed, so to say this is a Western “heresy” is a bit far-fetched, I am afraid.
Third, a heresy is a departure from a de fide infallible teaching. A case first can be made that the expressions “from the Father and the Son” and “from the Father through the Son” are equivalent because of the Son’s own procession from the Father. Everything the Son has is from the Father. The Father remains the sole origin of the Persons of the Trinity, so both statements contain the same theological truth yet just use different words to convey that one same truth. This can be seen in the writings of multiple early Church Fathers, both Latin and Greek, who use both forms. There was a brief reunion of sorts in 1439 at the council of Florence based on this profession of the same faith using different wording,
“The Greek prelates believed that every saint, precisely as a saint, was inspired by the Holy Spirit and therefore could not err in faith. If they expressed themselves differently, their meanings must substantially agree …] The Greek Fathers necessarily meant the same; the faiths of the two churches were identical; union was not only possible but obligatory”
Furthermore, his grace, bishop Kallistos Ware, an Eastern Orthodox bishop, has come to state,
“The filioque controversy which has separated us for so many centuries is more than a mere technicality, but it is not insoluble. Qualifying the firm position taken when I wrote The Orthodox Church twenty years ago, I now believe, after further study, that the problem is more in the area of semantics and different emphases than in any basic doctrinal differences”
Fourth, there is a difference in how the Latin and Greek languages are actually used which has caused more confusion on this issue: the Greek verb ἐκπορεύεσθαι and the Latin verb procedere are both commonly translated in English as “proceed”. The Greek verb ἐκπορεύεσθαι seems to indicate that the Spirit takes His origin from the Father in a principal and immediate manner. The Latin verb procedere, however, also leaves open the possibility of a procession from a mediate channel; this correponds to the Greek verb προϊέναι rather than ἐκπορεύεσθαι.
Fifth, the Eastern Churches in full communion with the bishop of Rome, the Eastern Catholic Churches, which perhaps you’d identify as the “Uniate” churches, do not use the Filioque in the Creed, yet they are in full communion with the Holy See.