Link to the Apostolic Canons: http://www.lyon.edu/webdata/users/jchiaromonte/Apostolic%20Canons.htm
Go to Canon 10. Then go to canon 45, and canon 46, and canon 65.
If any one shall pray, even in a private house, with an excommunicated person, let him also be excommunicated.
Canon XLV.
Let a bishop, presbyter, or deacon, who has only prayed with heretics, be excommunicated: but if he has permitted them to perform any clerical office, let him be deposed.
Canon XLVI.
We ordain that a bishop, or presbyter, who has admitted the baptism or sacrifice of heretics, be deposed. For what concord hath Christ with Belial, or what part hath a believer with an infidel?
Canon LXV.
If any clergyman shall strike anyone in a contest, and kill him with one blow, let him be deposed for his violence. If a layman do so, let him be excommunicated.
And which one of these says that anyone who believes in Filioque is a heretic; I missed that. As for Canon 65, while I admit that I have often become frustrated with the Orthodox, I deny ever killing anyone.