Myocardial reperfusion, while beneficial in restoring blood flow to ischemic myocardium, can also cause significant damage. This review discusses the dual nature of reperfusion, highlighting both its potential to save myocardial tissue and its risks of causing further injury. Reperfusion can lead to accelerated necrosis of irreversibly injured cells, cell swelling, the "no-reflow" phenomenon, hemorrhagic infarction, the calcium and oxygen paradox, oxygen-derived free radicals, and myocardial stunning. These phenomena can result in increased myocardial injury, ventricular dysfunction, and even heart failure. Reperfusion-induced necrosis occurs when oxygen and nutrients are reintroduced to ischemic tissue, which can cause a cascade of events leading to cell death. The "no-reflow" phenomenon, where blood flow does not return uniformly to all parts of the ischemic tissue, can contribute to infarct expansion and ventricular dysfunction. Hemorrhagic infarction, caused by reperfusion of damaged microvasculature, can lead to increased myocardial necrosis. The calcium paradox involves the sudden reintroduction of calcium to ischemic tissue, leading to cell swelling and contracture. The oxygen paradox involves the reintroduction of oxygen to anoxic tissue, leading to oxidative stress and cell damage. Oxygen-derived free radicals, such as superoxide anion and hydroxyl radicals, play a significant role in reperfusion injury. These radicals can damage cellular components, leading to cell death and dysfunction. Leukocytes also contribute to reperfusion injury by releasing cytotoxic products and causing inflammation. Free radical scavengers, such as superoxide dismutase and catalase, can help mitigate these effects. Myocardial stunning refers to the temporary dysfunction of the heart following reperfusion, characterized by prolonged postischemic depression of function and high energy phosphate stores. This condition can be reversed over time but may require prolonged pharmacologic or mechanical support. The review concludes that while reperfusion is generally beneficial, it must be performed as early as possible to maximize its benefits and minimize its risks. Future directions include the use of free radical scavengers, beta-adrenergic blockers, and calcium channel antagonists to improve reperfusion outcomes. The optimal approach to limiting infarct size involves a combination of prophylactic treatment, timely reperfusion, and the use of agents that minimize reperfusion injury.Myocardial reperfusion, while beneficial in restoring blood flow to ischemic myocardium, can also cause significant damage. This review discusses the dual nature of reperfusion, highlighting both its potential to save myocardial tissue and its risks of causing further injury. Reperfusion can lead to accelerated necrosis of irreversibly injured cells, cell swelling, the "no-reflow" phenomenon, hemorrhagic infarction, the calcium and oxygen paradox, oxygen-derived free radicals, and myocardial stunning. These phenomena can result in increased myocardial injury, ventricular dysfunction, and even heart failure. Reperfusion-induced necrosis occurs when oxygen and nutrients are reintroduced to ischemic tissue, which can cause a cascade of events leading to cell death. The "no-reflow" phenomenon, where blood flow does not return uniformly to all parts of the ischemic tissue, can contribute to infarct expansion and ventricular dysfunction. Hemorrhagic infarction, caused by reperfusion of damaged microvasculature, can lead to increased myocardial necrosis. The calcium paradox involves the sudden reintroduction of calcium to ischemic tissue, leading to cell swelling and contracture. The oxygen paradox involves the reintroduction of oxygen to anoxic tissue, leading to oxidative stress and cell damage. Oxygen-derived free radicals, such as superoxide anion and hydroxyl radicals, play a significant role in reperfusion injury. These radicals can damage cellular components, leading to cell death and dysfunction. Leukocytes also contribute to reperfusion injury by releasing cytotoxic products and causing inflammation. Free radical scavengers, such as superoxide dismutase and catalase, can help mitigate these effects. Myocardial stunning refers to the temporary dysfunction of the heart following reperfusion, characterized by prolonged postischemic depression of function and high energy phosphate stores. This condition can be reversed over time but may require prolonged pharmacologic or mechanical support. The review concludes that while reperfusion is generally beneficial, it must be performed as early as possible to maximize its benefits and minimize its risks. Future directions include the use of free radical scavengers, beta-adrenergic blockers, and calcium channel antagonists to improve reperfusion outcomes. The optimal approach to limiting infarct size involves a combination of prophylactic treatment, timely reperfusion, and the use of agents that minimize reperfusion injury.