Though HFpEF is characterized by a normal ejection fraction, this parameter is a rather poor index of the heart's contractile function.[28] Some studies have shown that metrics of load independent contractility (such as left ventricular stiffness) reveal diminished systolic function in HFpEF patients compared to healthy controls,[17] and are corroborated by tissue Doppler findings that reveal changes in longitudinal contraction and motion abnormalities.[29] While these systolic impairments may be minimal at rest, they become more exaggerated with increased demand, as seen in exercise.[30]