In the present work a complete set of energy levels, spontaneous radiative decay rates, and thermally averaged collision strengths are calculated for the first time for the five lowest electron configurations of Ca VIII, corresponding to 40 fine-structure energy levels. Collision data are calculated using the R-matrix approximation, and results are compared with earlier computations. The potential of Ca VIII lines for plasma diagnostics is shown. Ca VIII line emissivities are calculated and compared to observations of the Sun obtained with high-resolution spectrometers on board the Solar and Heliospheric Observatory (SOHO). Excellent agreement between predictions and observations is found, and Ca VIII is able to provide accurate measurements of Ca/Ne abundance, relevant for studies of the first ionization potential effect.