Anybody who is acquainted with sound Catholic theology knows that Solemn Magisterial pronouncements, that is ex cathedra dogmatic definitions by the Holy Roman Pontiff, are the only teachings of the Church that are guaranteed to be without any error at all, being protect by God the Holy Ghost.
There are, however, certain beliefs that have been understood to be heresy, from the very beginning of Christianity. Such beliefs are those that are contrary to the basic Christian Creed, the rudiments of faith,. This rule of Faith is the "Catholic Faith, whole and undefiled" as it was later defined in the Council of Florence when the Athanasian Creed was dogmatized.
What Must You Do To Get to Heaven?