Abstract: IP3 receptors are intracellular calcium channels, releasing calcium from the sarcoplasmic reticulum. In the heart, IP3 receptors of type 1 and 2 were found. These receptors predominate in atria, although they occur also in ventricles, as determined by real-time PCR and Western blot analysis. Single-immobilization stress was found to increase mRNA and/or protein levels of types 1 and 2 IP3 receptors in cardiac atria. However, in stellate ganglia, which innervate the heart, no changes in the mRNA of the type 1 IP3 receptors were observed after single-immobilization stress. In adrenal medulla, a moderate decrease in both mRNA and protein levels of IP3 receptors was observed after single-immobilization exposure. After repeated immobilization, mRNA and protein levels of types 1 and 2 IP3 receptors decreased significantly in all tested tissues. Our results point to different processing of the single stress in different tissues, while repeated stress results in rapid and significant decrease of the IP3 receptors.