Detrimental effects due to vasoconstriction of the vasculature
Generation of reactive oxygen species which could cause:
Toxic myocardial contractile dysfunction
Increased oxidative stress
Myocardial cell death
Earlier it was common practice to give supplemental oxygen for acute coronary syndrome and after percutaneous coronary interventions. This practice has been discontinued after publication of the DETO2X-AMI trial  and other similar studies which showed no benefit for supplemental oxygen in those with normal oxygen saturation.
Hofmann R, James SK, Jernberg T, Lindahl B, Erlinge D, Witt N, Arefalk G, Frick M, Alfredsson J, Nilsson L, Ravn-Fischer A, Omerovic E, Kellerth T, Sparv D, Ekelund U, Linder R, Ekström M, Lauermann J, Haaga U, Pernow J, Östlund O, Herlitz J, Svensson L; DETO2X–SWEDEHEART Investigators. Oxygen Therapy in Suspected Acute Myocardial Infarction. N Engl J Med. 2017 Sep 28;377(13):1240-1249.