[Relation of cardiac diastolic elasticity to its adaptation to loading]

The pump function of the isolated rat or guinea pig hearts was assessed at various functional loads. The diastolic left ventricular (LV) stiffness was determined by a ratio of a rise in LV pressure for a diastole to LV filling volume for a diastole. This index was several times lower for guinea pig's hearts as compared to the rat hearts at equal heart rate. It was associated with a higher cardiac output of guinea pig hearts at low left atrium filling pressure. The rat hearts, however, having a higher diastolic stiffness adapted better to increased resistance or elevated heart rate, preserved the cardiac output and markedly increased cardiac work. The data obtained suggest that LV diastolic stiffness is an important factor determining cardiac adaptation to various functional loads; its influence seems to be actualized through changes in the LV filling.