In what way was Swaggert a heretic?
Some would say (like the late R.C. Sproul), that his views deny the Trinity, or at least limited to “strictly to their being one in purpose, design and desire” (Swaggart's words). This varies with the traditional Christian teaching that the Trinity is also of one “substance.” Swaggart also held that God inhabits a “spirit body” with a specific location; orthodox Christianity insists that the deity is both omnipresent and a spirit.
Swaggart's sexual sins are (were), common to men and completely forgivable by God given true repentance. Those are not the issue. In my view it was his teaching doctrines as a "pastor" that vary from orthodox Christian that were the main issue.
I do wish God's peace upon his family given their personal loss.