Virtually all tissues have a requirement for glucose to function normally. Glycolysis is the major pathway of glucose metabolism and occurs in the cytosol of all cells. It can occur aerobically or anaerobically depending on whether oxygen is available. This is clinically significant because oxidation of glucose under aerobic conditions results in 32 mol of ATP per mol of glucose. However, under anaerobic conditions, only 2 mol of ATP can be produced. Aerobic glycolysis occurs in 2 steps. The first occurs in the cytosol and involves the conversion of glucose to pyruvate with resultant production of NADH. This process alone generates 2 molecules of ATP. If oxygen is available, then the free energy contained in NADH is further released via reoxidization of the mitochondrial electron chain and results in the release of 30 more mol of ATP per mol of glucose.However, when oxygen is in short supply, this NADH is reoxidized instead by reducing pyruvate to lactate. This severely limits the amount of ATP formed per mole of glucose oxidized when compared with aerobic glycolysis. In situations where there is an imbalance of oxygen usage and oxygen delivery, for example in sepsis or heart failure, anaerobic glycolysis occurs and results in lactate accumulation and results in inefficient glucose usage and inadequate ATP production.