Really? What heresy was rampant in Gaul, a large section of the Patriachate of Rome, in the fourth through eighth centuries, and why didn't the Popes of Rome deal with it, or have their legates raise the issue at one of the Ecumenical Councils held during that time?
This is a good explanation of your "heresy" question.
http://www.ask.com/wiki/Christianity_in_the_4th_century?o=2800&qsrc=999&ad=doubleDown&an=apn&ap=ask.com
The Church was in its very early stages.
It took years for information to disseminate throughout the empire and church. I can even imagine that SOME information never did get to some places.
Here is a good explanation of your second question.
http://www.ask.com/wiki/Catholic_Ecumenical_Councils?o=2800&qsrc=999&ad=doubleDown&an=apn&ap=ask.com