For the Catholic Church, the Orthodox Churches are sister Churches with true apostolic succession, valid sacraments, and who hold to the orthodox catholic faith delivered to the saints. We view Orthodox Christians as already being in an imperfect communion with the Catholic Church - imperfect yet so profound that we invite them to share our Eucharist. The Orthodox are not heretics and individual Orthodox Christians are not even seen as formal schismatics.
For many, though not all, among the Orthodox, on the other hand, Catholics are heretics who have distorted and perverted the orthodox faith, and our eucharist is an empty show devoid of grace. For other Orthodox Christians, our Eucharist is a true participation in the body and blood of Christ and we, while heretodox on some points, are more or less orthodox. It really varies - the spectrum couldn’t be more extreme in my experience.