In 1054, papal legate Humbert of Silva Candida excommunicates the Patriarch of Constantinople, Michael Celarius; Celarius excommunicates him right back; it's all very flashy and dramatic sounding. Historiographically, it's "good enough" to date the division of the Chalcedon-accepting Church into a West and East.
When we call it a "schism", though, this is a theologically weighty word. A schism is a division in the communion of the Body of Christ. A heresy, on the other hand, is a dogmatic/doctrinal error. At the Council of Chalcedon in 451, for example, the miaphysites were declared heretics--they were kicked out of the Communion of Christ, not seen to be a separated part of it.
Now, there were and are important theological differences between West and East. Obviously the most significant one is papal primacy. In the Middle Ages, whether the Eucharist bread ought to be leavened (East) or not (West) was paramount. Some of the issues that get more airplay today (the "filioque", or whether the Holy Spirit proceeds "from the Father and the Son" or "from the Father through the Son") and some that you might think would be SUPER important in the context of late medieval theology (purgatory) might pop up in discussions at the Council of Florence in 1439, when Western and Eastern delegates met to talk about consolidating again (unsuccessfully)--but they were hardly central. This was a matter of Church hierarchy, not dogma.
The running attitude in the Middle Ages tends to be grudging allowance, a low-level desire for reconciliation without much zeal for making it happen, the occasional declaration of heresy for posturing's sake, some bad clashing of authority in the Crusader states--but mostly, live and let live. In places where Latin and Greek Christians coexisted, especially Cyprus, there was a notable sharing of art programs for church frescoes. French (Latin) families patronize Greek churches; Greek artists create mosaics in Latin and Greek iconography for Latin churches. This doesn't mean Latin domination was welcomed by Greek Christians (on Crete, apparently the Greeks were pretty happy when the Ottomans showed up in the 17th century!). But there was grudging coexistence-with-exploitation, which is not exactly the medieval Christian treatment of heretics.
I'm less familiar with the Greek side of things, but when you look at various levels of religious positions in the West--it's almost shocking how little attention is paid to the East, especially by women and men who otherwise seem to have an astute sense of the religious world. Visionaries on voyages to the underworld spew vitriol about the priests and monks and even popes they see in hell. From the 12th century, carefully and cleverly obedient holy women are the PR frontline against heretical movements in western Europe. They absolutely have access to knowledge of the Greek East. Where are the patriarchs in their visions and prophecies? Do they castigate eastern bishops? Non frah.
The Great Schism also included a disagreement on the use of icons. What was the disagreement and how were they used? This might be a slightly dumb question, but both Orthodox Christians and Catholics have representations in picture or statue form.