Doing a little bit of research into official definitions of heresy, especially as according to the Catholic Church, brought up some interesting points I’d never heard before. Catholic Canon law is extremely complex.

1. Technically, you can only be considered a heretic as long as you profess to still be a Catholic Christian. This means that you still are into Jesus, and the Church in general, but that your views in particular about certain doctrines differ from those of the orthodoxy.
2. Somebody who rejects the authority of the Church, but not of Jesus or his teachings is considered in schism. I think that it’s ordinarily churches that are considered in schism and when they break away from submitting to the will of Rome and the authority of the Pope.
3. If you reject both the Church, and more importantly Jesus, you’re considered to be an apostate, or in apostasty.
4. Heresy, apostasy and schism all automatically land you in the excommunication box.
5. From the Catholic Encyclopedia:
   The apostate a fide abandons wholly the faith of Christ either by embracing Judaism, Islamism, Paganism, or simply by falling into naturalism and complete neglect of religion; the heretic always retains faith in Christ. Heresy also differs from schism. Schismatics, says St. Thomas, in the strict sense, are they who of their own will and intention separate themselves from the unity of the Church.
6. Heresy is considered to be a sin because it damages “faith” which is considered to be the greatest possession of man. “Privation of faith is therefore the greatest evil, and deliberate rejection of faith is the greatest sin.”
7. Here may be of “material” or “formal.” Material heresy, considered to be lesser, basically implies that free will is not involved in the creation or continuation of tenets which violate the orthodox view. Things like ignorance or misunderstanding of the true tenets of the faith may bring about material heresy, while formal heresy involves an act of will, driven by motives which may include “intellectual pride or exaggerated reliance on one’s own insight; the illusions of religious zeal.” (No wonder they suppressed gnostics so fiercely.)
8. For a heresy to be considered formal, it also has to display “pertinacity” or you must stubbornly adhere to it. “For as long as one remains willing to submit to the Church’s decision he remains a Catholic Christian at heart and his wrong beliefs are only transient errors and fleeting opinions.”
9. Heresy didn’t become punishable by death until 382 CE, and the first execution for heresy is said to have been of Priscillian in 385. Executions for heresy were usually carried out by the civil authorities, so the blood was not on the hands of the Church.
10. Before Constantine converted the Roman Empire to Christianity (around, 325, I’ll have to look up the date…), the only punishment which the Church gave for heresy was excommunication. This meant you were exiled from the community of the Church, and could not receive any sacraments or other rights of a Christian.
11. When particular heresies got to be too popular or gained too many followers, the Church would usually formally denounce them at one of their regional or ecumenical (world-wide) synods or councils.
12. Between 1184-1243 CE, a series of binding church councils promoted the rooting out of heresy, and established that every church parish was to have an official Inquisitor. Inquisitions were initially handled by local authorities, but after 1230, they came under the direct control of Papal inquisitors, who were usually monks of the Dominican Order
13. The Inquisition was a formal office within the Church of Rome. It’s modern equivalent is the Congregation for the Doctrine of the Faith
14. The first Inquisition was against the Cathars in southern France who are said to have been a gnostic group. Also, the Albigensian Crusade was initiated from 1209-1229 to further destroy the Cathars.
15. The investigation procedure for Papal Inquisitions when they came to town is a real hoot and worth reading. Here’s a great bit:
    The inquisitorial trial generally favored the prosecution (the Church). The defendant would be allowed a lawyer, but if the defendant was convicted, the lawyer would lose his ability to practice. Therefore most lawyers never took the chance of defending a potential heretic. The trials were conducted in secret with only the inquisitors, the defendant and some inquisitorial staff to take notes. Inquisitors sequestered all of the property of the defendant. The defendant was not told the charges, but was always invited to confess, only guessing what for. The accused was expected to self-incriminate and did not have the right to face and question the accuser. It was acceptable to take testimony from criminals, persons of bad reputation, excommunicated people, and convicted heretics. Blood relationship did not exempt one from the duty to testify against the accused. Sentences could not be appealed once made. The inquisitor could keep a defendant in prison for years before the trial to obtain new information.
16. Information or confessions gained by torture were not admissible at first, but that was changed in 1252. They were forbidden to use methods that drew blood, and so were consequently milder than those used by secular courts of the time.
17. This bit about sentencing is also pretty good:
    Once the trial was concluded the results might take years to be revealed, during which time the defendant stayed in prison. The inquisitors would save up the cases and announce them at once in a public ceremony called, in Latin, sermo generalis, or “general sermon”. Punishment could range from a long pilgrimage for first offenders, wearing a yellow cross for life, confiscation of property, banishment, public recantation, or long-term imprisonment, a method of punishment the inquisition pioneered that is still in use today. Burning at the stake was only for the most serious cases, including repeat offenders and unrepentant heretics. Execution was done not by the Church, which was forbidden to kill, but by secular officials. Life imprisonment or death was always accompanied by the confiscation of all the accused’s property.