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Little research explores the effect of heat on the isotopic composition of ostrich eggshell (OES), though several studies use stable isotopes in OES to assist in paleoclimatic reconstruction. Archaeological OES often shows signs of heat exposure, though distinguishing lower-temperature exposure remains challenging. This controlled study uses modern OES heated in an electric kiln to examine if exposure to low through high degrees of heat shifts δ13C, δ15N, and δ18O values in the organic and mineral components of ostrich eggshell. Results indicate that the total organic portion of the shell conserves original isotopic signatures with exposure below ~220 ◦C, while the mineral portion conserves signatures up to 500 ◦C. Additionally, the study provides C:N ratios as a reliability criterion for the organic portion of archaeological OES. Data produced in this study allows for a more discriminating selection of archaeological samples for paleoclimatic reconstructions.