Background: The pathophysiology of heart failure with preserved ejection fraction is not well understood, but evidence strongly suggests involvement of microvascular dysfunction. We studied the myocardial oxygenation reserve as a direct marker of coronary vascular function and its relation to myocardial deformation and tissue characteristics by cardiovascular magnetic resonance (CMR). Methods: In a dual-center case-control study, patients with heart failure and preserved ejection fraction (>50%) and healthy controls older than 50 years underwent quantitative CMR for ventricular volumes and functional assessment with feature tracking, as well as tissue characterization (T1, T2, extracellular volume). Coronary vascular function was measured by oxygenation-sensitive (OS)–CMR of the myocardial oxygenation response to a vasoactive breathing maneuver. Results: Twenty-nine patients completed the CMR exam. Compared with cutoffs derived from 12 control subjects, circumferential peak strain was attenuated in 97% of patients. Native T1 was elevated in 93%, extracellular volume was elevated in 83%. Sixty-six percent of patients revealed either regional or global myocardial edema, defined by an increased myocardial T2. An attenuated global myocardial oxygenation reserve (<4.4%) was observed in 96% of the patients (1.7±3.9% versus 9.1±5.3% in controls, P <0.001). This was correlated with septal wall thickness (r=−0.54, P =0.003), edema (myocardial T2; β=−0.26% oxygenation-sensitive/ms [95% CI, −0.49 to −0.03], P =0.029), and reduced diastolic strain rate (β=1.50% oxygenation-sensitive/s ^-1 [95% CI, 0.06–2.90], P =0.042). Conclusions: In patients with clinical heart failure with preserved ejection fraction, vascular dysfunction as measured by an attenuated myocardial oxygenation reserve is associated with myocardial edema, a thicker septum, and diastolic dysfunction. A quantitative comprehensive CMR exam including oxygenation-sensitive–CMR allows for comprehensive imaging-based phenotyping of heart failure with preserved ejection fraction.