Intravenous insulin therapy is used in diabetic patients at the acute phase of coronary syndrome (ACS). However, hyperglycemia in diabetic patients is a powerful predictive factor for patient outcome as it is associated with a doubling of in-hospital mortality and poor long-term prognosis. Recent studies involving non-diabetic patients show that even mild hyperglycemia in the setting of ACS is also a predictive factor of in-hospital mortality. Moreover, the new entity called impaired fasting glucose (IFG) (6.1 to 7 mmol/L) is not only an independent factor of mortality for coronary patients, but very recently has also been associated with a doubling of the risk of in-hospital mortality in the setting of ACS. Admission as well as follow-up glycaemia are fundamental parameters in ACS on the one hand for their prognostic value, and on the other end as a diagnostic tool in determining the presence of diabetes or IFG.