Acute coronary syndrome is the result of a significant stenosis or occlusion of infarct-related artery, which is usually caused by large thrombus as the consequence of sudden rupture of a vulnerable plaque. The occlusion or significant stenosis identified on an angiogram is mainly composed of thrombus (angiographic culprit lesion) however the site of plaque rupture or the site of maximum necrotic core is usually located a few millimeters proximal to it.20 patients with non-ST-elevation acute coronary syndrome and 20 patients with ST-elevation myocardial infarction who had TIMI-3 flow re-established (with or without thromboaspiration) in infarct-related artery and underwent angiographically-guided stent implantation were enrolled and assessed in this study. Culprit lesions prior to stent implantation and treated segments of infarct-related arteries were assessed by intravascular ultrasound, virtual-histology intravascular ultrasound and optical coherence tomography (blinded to the operator).With the use of these imaging modalities culprit lesions were studied in detail as well as the phenomenon of longitudinal geographic miss, which was defined as the presence of a vulnerable plaque in the reference segments of the treated segment of infarct-related artery. Using virtual-histology intravascular ultrasound longitudinal geographic miss was confirmed in 70% of patients with non-ST-elevation acute coronary syndrome and in 35% of patients with ST-elevation myocardial infarction. With the use of optical coherence tomography geographic miss was confirmed in 10% of patients with ST-elevation myocardial infarction and in none of the non-ST-elevation acute coronary syndrome patients. The use of intravascular ultrasound and optical coherence tomography in patients with acute coronary syndrome is safe and feasible and provides the operator with additional information for the optimization of primary percutaneous coronary intervention.