Coronary artery ectasia (CAE) is defined as diffuse or focal dilation of a coronary artery segment exceeding 1.5 times the diameter of the adjacent normal segment. It is found in 1-5% of patients undergoing coronary angiography. The most common association is atherosclerosis (~50% of cases), where enzymatic degradation of the media and adventitia by matrix metalloproteinases leads to vessel dilation rather than stenosis. Other causes include Kawasaki disease (leading cause in younger patients), connective tissue disorders (Marfan, Ehlers-Danlos), vasculitis (polyarteritis nodosa, Takayasu), and iatrogenic (post-PCI). The dilated segments promote blood stasis and turbulent flow, increasing thrombotic risk. Markis classification grades severity: Type I (diffuse ectasia of 2-3 vessels), Type II (diffuse ectasia of one vessel + localized of another), Type III (diffuse ectasia of one vessel), Type IV (localized/segmental ectasia).