Technically, the term "heretic" is usually reserved to a Catholic who denies a dogma of the faith. Persons who were never Catholics aren't usually considered to fall under that classification.
The Catholic Church has no trouble calling anyone who is validly baptized (which includes almost all baptized Protestants) a "Christian". I believe Vatican II said that pretty clearly.
This is not what Vatican I says which states:
This true catholic faith, outside of which none can be saved, which I now freely profess and truly hold,...
Didn't we once talked about consistency?