Matrix metalloproteinases (MMP) are enzymes that degrade extracellular matrix (ECM) proteins and regulate both their accumulation and composition. The MMP are involved in the atherosclerotic process since they contribute to the formation of the plaque and its subsequent rupture. This last step triggers the myocardial ischemia that will be clinically reflected as an acute coronary syndrome (ACS). Thus, MMP activity is a key to whether ACS develops or not. With an elevated transcription rate of the genes that codify these proteinases comes a higher enzymatic activity. This explains that if a polymorphism in the mentioned genes modifies transcription, there could be a predisposition to developing ACS. Several studies reveal that certain genetic variations in MMP-1, -2, -3, -7, -8, -9, -12, and -14 have an important role either as risk factors or as protective factors for the expression of ACS.