Low-molecular-weight heparins (LMWHs) have shown equivalent or superior efficacy and safety to unfractionated heparin as antithrombotic agents for the treatment of patients with acute coronary syndromes (ACS). In patients with unstable angina and non-ST segment elevation myocardial infarction (MI), many data support the use of the LMWH enoxaparin to reduce cardiovascular events and death. LMWHs also appear more effective than unfractionated heparin in reducing the composite end point of acute MI, recurrent ischemia, or death in patients with ST segment elevation MI, and can also be used effectively in patients undergoing thrombolysis reperfusion and percutaneous coronary intervention. However, the various LMWH preparations should not be used interchangeably. Each LMWH is a pleiotropic biological agent with a unique chemical, biochemical, biophysical, and biological profile, and it displays a unique pharmacodynamic and pharmacokinetic profile. As a result, LMWHs are not equipotent in preclinical assays or equivalent in terms of their clinical efficacy and safety. Therefore, it is essential that new, emerging, generic versions of LMWHs demonstrate clinical equivalence, in specific indications, with the existing approved LMWHs. This article highlights the chemical, biological, and pharmacological differences between the LMWH preparations that may result in different clinical outcomes during the treatment of patients with acute coronary syndromes.