Although left atrial (LA) dysfunction is common in heart failure with preserved ejection fraction (HFpEF), its functional implications beyond the reflection of left ventricular (LV) pathology are not well understood. The aim of this study was to further characterize LA function in HFpEF patients. We performed cardiac magnetic resonance myocardial feature tracking in 22 patients with HFpEF and 12 patients without HFpEF. LA reservoir strain, LA conduit strain, and LA booster pump strain were quantified. Peak oxygen uptake (VO2max) was determined. Invasive pressure-volume loops were obtained to evaluate LV diastolic properties. LV early filling was determined from LV volume-time curves as derived from cardiac magnetic resonance. LA reservoir and conduit strain were significantly lower in HFpEF (LA reservoir strain, 22±7% versus 29±6%, P=0.04; LA conduit strain, -9±5% versus -15±4%, P<0.01). Patients with HFpEF showed lower oxygen uptake (17±6 versus 29±8 mL/(kg min); P<0.01). Strain measurement for LA conduit function was strongly associated with VO2max (r=0.80; P<0.01). On multivariable regression analysis, LA conduit strain emerged as strongest predictor for VO2max even after inclusion of LV stiffness and relaxation time (β=0.80; P<0.01). LA conduit strain correlated with the volume of early ventricular filling (r=0.67; P<0.01), but not LV stiffness constant β (-0.34; P=0.051) or relaxation constant τ (r=-0.33; P=0.06). Cardiac magnetic resonance myocardial feature tracking-derived conduit strain is significantly impaired in HFpEF and associated with exercise intolerance. Impaired conduit function is associated with impaired early ventricular filling, as potential mechanism leading to impaired oxygen uptake. Our results propose that impaired LA conduit function represents a distinct feature of HFpEF, independent of LV stiffness and relaxation. URL: http://www.clinicaltrials.gov. Unique identifier: NCT02459626.