There is no heresy unless the Church, in an Ecumenical Council, proclaimes it to be such. To the best of my knowledge neither side is in heresy, although some individual fathers on both sides, and at different times, accused the other side of heresy.
yes -- just as we both (incorrectly) accused the Monophysites of being, well, Monophysites and being heretical. Language CAN be very tricky, eh!! Especially when one uses words like hypotheosis etc. :)