Relaxation and diastole of the heart

In the present review, we adopted the viewpoint of the physiologist looking at the global function of the heart, during relaxation and diastole, as an integrated muscle-pump system. We first focused our attention on properties of relaxation and diastole at the subcellular (SR, contractile proteins), cellular, and multicellular scales of cardiac muscle and then at the scale of the ventricle and intact global heart. At each lower scale we derived properties from experimental facts and examined the extent to which these properties could be extrapolated conceptually to the higher scale. From this muscle-pump approach, we learned that a general and fundamental property of relaxation of the heart as a muscle-pump system is load dependence, i.e., the mutually independent behavior of the time patterns of slow force decline and pressure fall and of rapid lengthening and rapid filling. Load dependence is found at all hierarchic scales, irrespective of whether it is examined under strictly isotonic-isometric or isom...