Acute coronary syndrome without ST-segment elevation (NSTE-ACS) is by far the most frequent acute coronary syndrome (ACS) in the western world. In most of the cases, it is caused by a clearly identifiable culprit lesion, configuring a significant angiographic stenosis (>70%), with flux limitation and typical aspects of unstable plaque (thrombosis). In these cases, the one and only treatment is stent implantation. In a small percentage of patients (10-15%), NSTE-ACS is caused by an angiographically intermediate lesion (40-70%). This lesion is identifiable as culprit, but without the typical signs of unstable plaque.