Calcium is a crucial signal molecule in the cardiovascular system. Calcium (Ca ²⁺) acts as a second messenger via changes in intracellular Ca ²⁺ levels through the actions of calcium channels and pumps. However, it is now well known that calcium may also be an extracellular first messenger through a G-protein-coupled receptor that senses extracellular Ca ²⁺ concentration, the calcium-sensing receptor (CaR). The CaR is one of the key players in extracellular calcium homeostasis, but besides being expressed in the major organs involved in calcium homeostasis, the parathyroid gland, kidney and intestine, the CaR has also been found to be functionally expressed in other tissues. Although several studies demonstrated the CaR in heart and blood vessels, exact roles of the receptor in the cardiovascular system still remain to be elucidated. This review will summarize the current knowledge on the expression and possible functions of the CaR in the cardiac tissue.