Hearon CM, et al. - Given that cases with heart failure (HF) with reduced ejection fraction exhibit impaired time needed to increase oxygen utilization to meet metabolic demand (V̇O₂ kinetics), which also represents an independent risk factor for HF mortality, researchers investigated whether V̇O₂ kinetics are slowed during submaximal exercise in HF with preserved ejection fraction (HFpEF) in this study with 18 HFpEF patients (68±7 years, 10 women) and 18 healthy controls (69±6 years, 10 women). They also determined if slower V̇O₂ kinetics are associated with impaired peripheral oxygen extraction among participants. Submaximal and peak exercise testing was completed by the participants. During exercise, they evaluated cardiac output (acetylene rebreathing, Q̇c), ventilatory oxygen uptake (V̇O₂, Douglas bags) and arterial-venous O₂ difference derived from Q̇c and V̇O₂. Findings revealed slowed V̇O₂ kinetics in HFpEF, and this was associated with impaired peripheral oxygen utilization. HFpEF patients with peripheral limitations to submaximal exercise capacity could be identified by mean response time, which could be a target for therapeutic intervention.