Primary heat stabilizer categories include Lead (both inorganic and organic salts), "Mixed Metal" salts of organic acids (Barium/Cadmium-no longer allowed/Calcium/Zinc, and Organotin carboxylates or mercaptoesters (Methyl,Butyl,Octyl Tins).
Secondary, or co-stabilizers, include epoxidized soybean oil and epoxidized tallate esters, alkyl/aryl phosphites,
phenolic and hindered amine antioxidants.
A newer class of all-organic, metal-free primary stabilizers is beginning to make inroads in the marketplace--
including (mostly proprietary) uses of certain nitrogen heterocycle compounds and ester thiols.
More detailed info is available in books devoted to this subject----like the Encyclopedia of PVC edited by Len Nass,
or Ed Wickson's "Handbook of PVC Compounding"