PROSPECT II study evaluated the use of near-infrared spectroscopy (NIRS) with intravascular ultrasound (IVUS imaging) to identify the composition of non-culprit plaques in AMI patients, and to determine long term outcomes. 898 AMI patients (22.2% STEMI, 77.8% NSTEMI) were enrolled and a total of 3,629 untreated non-culprit lesions were identified. The mean clinical follow-up duration was 3.7±0.9 years and adverse events from untreated non-culprit lesions occurred in 8% of patients (MI in 3.6%, progressive angina in the remainder). The mean baseline diameter stenosis in these lesions with events was 46.9% and lipid rich plaque as well as large plaque burden were independent predictors of non-culprit events. This is a provocative study which raises many questions. However, randomized controlled trials will be needed in order to delineate which therapies, if any, will reduce the adverse events associated with lipid rich plaque in ACS patients. The fact that 38% of “non-significant" lesions by angiography had MLA < 4.0, speaks to the need for greater utilization of invasive hemodynamic and/or imaging to accurately determine lesion significance.