How the heart relaxes

Normal functioning of the heart is dependent on its ability both to contract and relax. Heart contraction is a complex process that is initiated by an increase in intracellular calcium, which results in myosin binding to actin and myosin movement of the actin filament. Relaxation is reliant on removal of calcium from the contractile filaments, which in turn is dependent on the availability of ATP. If the heart does not relax properly, it cannot fill with blood during diastole, which subsequently compromises its ability to pump sufficient quantities of blood to the body. The inability of the heart to relax properly can cause heart failure. Therefore, reduced ATP levels such as are observed in heart failure may contribute to impairments in heart diastolic function. This paper reviews the mechanism of cardiac muscle contraction and relaxation as well as the role of relaxation in heart disease.