Angioscopy allows direct visualization of the coronary artery lumen and provides detailed information regarding the surface characteristics of the vessel wall and specific lesions causing acute coronary syndromes. Disruption of a plaque, ulceration, tears, fissures, lipid-rich or fibrous lesions, and luminal or mural thrombus can be readily detected in vivo. Characterization of culprit lesions in various coronary syndromes reveals the different mechanisms of ischemia. The predominant lesion in acute myocardial infarction is an ulcerated, yellow plaque with thrombus. In unstable angina, different substrates can be seen, from the lipid-rich lesion with thrombus to the fibrous smooth plaque, reflecting a varied physiopathology. Because of its ability to detect superficial lipid pools, angioscopy may be valuable for the detection of vulnerable plaques.