In published post-mortem pathological studies, more than two-thirds of acute coronary events are associated with the rupture of lipid-rich, voluminous, and outwardly remodelled plaques covered by attenuated and inflamed fibrous caps in the proximal part of coronary arteries. Superficial erosion of the plaques is responsible for most of the remaining events; the eroded plaques usually do not demonstrate much lipid burden, do not have thin fibrous caps, are not positively remodelled, and are not critically occlusive. Both noninvasive and invasive imaging studies have been performed to clinically define the plaque characteristics in acute coronary syndromes in an attempt to identify the high-risk plaque substrate susceptible to development of an acute coronary event. Optical coherence tomography (OCT)--an intravascular imaging modality with high resolution--can be used to define various stages of plaque morphology, which might allow its use for the identification of high-risk plaques vulnerable to rupture, and their amenability to pre-emptive interventional treatment. OCT might also be employed to characterize plaque pathology at the time of intervention, to provide a priori knowledge of the mechanism of the acute coronary syndrome and, therefore, to enable improved management of the condition.