A class of heterocyclic compounds that include a three-ring fused structure. Both aromatic or non-aromatic ring structures are included in this category.

Synonyms: 0, Heterocyclic Compounds, 3-Ring, 3-Ring Heterocyclic Compounds, Three Ring Heterocyclic Compounds, Heterocyclic Compounds, 3 Ring, Fused Heterocyclic Compounds, Three-Ring, Heterocyclic Cpds, 3 Ring, Fused Heterocyclic Compounds, Three Ring