Tang et al. demonstrated that increased plasma levels of MMP2 and MMP9 in patients with coronary heart diseases (CHD) suggest the instability of the atherosclerotic plaque in correlation to the severity of ACS, and may serve as good indicators for the prediction of ACS and diagnosis of chronic total occlusion (CTO) of the coronary artery [162]. Here, MMP9 is linked to coronary artery disorder.