One of the most important factors that affect the developmental competences of mammalian somatic cell nuclear transfer (SCNT) embryos is artificial activation of reconstructed oocytes (clonal cybrids). However, calcium signal transduction in a cytosol of such oocytes that has been initiated incorrectly by physical or chemical activating factors (electric pulses or specific ionophore antibiotics) can stimulate not only the development of cloned embryos. It can also induce apoptotic cell death following considerable elevation in intracellular calcium concentration and thereby excitotoxicity of Ca2+ ions. Therefore, the basic objective of this paper is to present the current knowledge on the mechanisms regulating biochemical and biophysical proapoptotic changes within SCNT embryos via the process of excitotoxic calcium signal transmission resulting from an improper artificial activation of clonal cybrid.