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Peak oxygen uptake (VO2) is diminished in patients with heart failure with preserved ejection fraction (HFpEF) suggesting impaired cardiac reserve. To test this hypothesis, we assessed the haemodynamic response to exercise in HFpEF patients.Eleven HFpEF patients (73 ± 7 years, 7 females/4 males) and 13 healthy controls (70 ± 4 years, 6 females/7 males) were studied during submaximal and maximal exercise. The cardiac output (Qc, acetylene rebreathing) response to exercise was determined from linear regression of Qc and VO2 (Douglas bags) at rest, ∼30% and ∼60% of peak VO2, and maximal exercise. Peak VO2 was lower in HFpEF patients than in controls (13.7 ± 3.4 vs. 21.6 ± 3.6 mL/kg/min; P < 0.001), while indices of cardiac reserve were not statistically different: peak cardiac power output [CPO = Qc × mean arterial pressure (MAP); HFpEF 1790 ± 509 vs. controls 2119 ± 581 L/mmHg/min; P = 0.20]; peak stroke work [SW = stroke volume (SV) × MAP; HFpEF 13 429 ± 2269 vs. controls 13 200 ± 3610 mL/mmHg; P = 0.80]. The ΔQc/ΔVO2 slope was abnormally elevated in HFpEF patients vs. controls (11.2 ±3.6 vs. 8.3 ± 1.5; P = 0.015).Contrary to our hypothesis, cardiac reserve is not significantly impaired in well-compensated outpatients with HFpEF. The abnormal haemodynamic response to exercise (decreased peak VO2, increased ΔQc/ΔVO2 slope) is similar to that observed in patients with mitochondrial myopathies, suggesting an element of impaired skeletal muscle oxidative metabolism. This impairment may limit functional capacity by two mechanisms: (i) premature skeletal muscle fatigue and (ii) metabolic signals to increase the cardiac output response to exercise which may be poorly tolerated by a left ventricle with impaired diastolic function.