 Oxygen therapy has been used for decades in order to reduce the risk of myocardial infarction and stroke in patients undergoing vascular surgery and pre-existing co-morbidities in the belief that increased inspired oxygen increases oxygen delivery to tissues, thereby reducing the risk for hypoxia and cell death. However, several studies published recently have questioned the routine use of high inspired oxygen concentration hyperoxia to improve oxygen delivery, specifically in the neonatal period but possibly even following myocardial infarction. This could be explained by the fact that increasing inspired concentrations of oxygen cause vasoconstriction in cerebral and coronary arteries, thereby reducing blood flow. Additionally, increased oxygen causes excessive production of reactive oxygen species ROS, and repercussion injury from oxidative stress. The latter can lead to apoptosis cell death in myocardial or cerebral neurons. Despite the high risks of administering oxygen when not needed, it is routinely used in hospitals all over the world without a doctors prescription. 