Background The impact of hyperoxia, that is, supraphysiological arterial partial pressure of O, on myocardial oxygen balance and function in stable multivessel coronary artery disease (CAD) is poorly understood. In this observational study, we assessed myocardial effects of inhalational hyperoxia in patients with CAD using a comprehensive cardiovascular magnetic resonance exam. Methods and Results Twenty-five patients with stable CAD underwent a contrast-free cardiovascular magnetic resonance exam in the interval between their index coronary angiography and subsequent revascularization. The cardiovascular magnetic resonance exam involved T1 and T2 mapping for tissue characterization (fibrosis, edema) as well as function imaging, from which strain analysis was derived, and oxygenation-sensitive cardiovascular magnetic resonance imaging. The latter modalities were both acquired at room air and after breathing pure O by face mask at 10 L/min for 5 minutes. In 14 of the 25 CAD patients (56%), hyperoxia induced poststenotic myocardial deoxygenation with a subsequent oxygenation discordance across the myocardium. Extent of deoxygenation was correlated to degree of stenosis (=-0.434, =0.033). Hyperoxia-associated poststenotic deoxygenation was accompanied by ipsiregional reduction of diastolic strain rate (1.39±0.57 versus 1.18±0.65; =0.045) and systolic radial velocity (37.40±17.22 versus 32.88±13.58; =0.038). Increased T2, as well as lower cardiac index, and defined abnormal strain parameters on room air were predictive for hyperoxia-induced abnormalities (<0.05). Furthermore, in patients with prolonged native T1 (>1220 ms), hyperoxia reduced ejection fraction and peak strain. Conclusions Patients with CAD and pre-existent myocardial injury who respond to hyperoxic challenge with strain abnormalities appear susceptible for hyperoxia-induced regional deoxygenation and deterioration of myocardial function. Clinical Trial Registration URL: http://www.clinicaltrials.gov. Unique identifier: NCT02233634.