The organism can survive by the contraction and relaxation of muscles, which are excitable tissues. The Ca2+ ion plays a key role in both contraction and relaxation of muscles. Contraction and relaxation of muscle cells can be achieved by regulating the intracellular concentration of Ca2+ ion. Regulation of Ca2+ ion concentration is accomplished by means of electrochemical gradient and membrane ion pumps. Diastolic and systolic dysfunctions are a common condition representing cardiac muscle contraction and relaxation problems. For this reason, it is important to know clearly the contraction and relaxation mechanisms in the heart and all muscles, and the roles of Ca2+ ions in these mechanisms. In this section, the key roles of Ca2+ ions and pumps, which have an important role in maintaining body homeostasis, on muscle contraction and relaxation and the regulation of Ca2+ ion concentrations will be discussed.