Description: This article discusses temperature-dependent structural heterogeneity in calcium silicate liquids. X-ray diffraction measurements performed on aerodynamically levitated CaSiO3 droplets have been interpreted using a structurally heterogeneous liquid-state model. When cooled, the high-temperature liquid shows evidence of the polymerization of edge shared Ca octahedra. Diffraction isosbestic points are used to characterize the polymerization process in the pair-distribution function. This behavior is linear in the high-temperature melt but exhibits rapid growth just above the glass transition temperature around 1.2Tg. The heterogeneous liquid interpretation is supported by molecular-dynamics simulations which show the CaSiO3 glass has more edge-shared polyhedra and fewer corner shared polyhedra than the liquid model.